Navigate Maps, Capture and Report Data, and Perform GIS Analysis ArcGIS for iPhone

Esri has expanded its mobile GIS platform to support the iPhone. ArcGIS for iPhone will include both a free downloadable application from Apple's App Store and an API for iPhone developers to build focused mapping solutions.

ArcGIS for iPhone leverages capabilities from ArcGIS Online to provide a seamless and easy user experience. Users can navigate maps and discover assets from Web services, as well as capture new data from the field and send information back to the server. This allows ArcGIS Server customers to leverage their GIS investment in the iPhone by using the device to access their own corporate data. ArcGIS for iPhone also promotes collaboration and information sharing between multiple users in the field. For example, field users can create and share status updates with others to communicate and work more efficiently.

ArcGIS Application for iPhone

ArcGIS for iPhone is a native iPhone application that serves as a mobile gateway into the ArcGIS system. This system will include access to services available through ArcGIS Online or on-site ArcGIS Server deployments hosting your corporate authoritative data. The ArcGIS for iPhone application consumes maps authored and hosted through ArcGIS Server. These maps contain not only data but also functionality (query, find, geoprocessing tasks, etc.).

The ArcGIS for iPhone application includes the following capabilities:

• Map navigation using native iPhone gestures
• Search, Identify, and Measure tools
• Collection/Update features and attributes (these will be available after initial release)
• GIS analysis through access to geoprocessing tasks (this will be available after initial release)
• GIS information sharing with other iPhone users

ArcGIS API for iPhone

The ArcGIS API for iPhone is built on Objective-C/Cocoa, the development framework for iPhone. It provides developers and Esri partners with the opportunity to create their own custom, spatially enabled iPhone applications to address their end-user and business requirements. It also lets organizations extend their solution products to iPhone's large user base and brand their iPhone applications with a custom logo, look and feel, etc.

The API is designed to work with and use Web services available from ArcGIS Server and ArcGIS Online, and its architecture is similar to Esri's ArcGIS Web Mapping APIs for JavaScript, Flex, and Silverlight. It will also follow the same ArcGIS API release and deployment pattern: easy online access/download with periodic updates.

Developers and Esri partners will use the API to create their own applications for both external and internal use. They can also easily build iPhone applications that work with their own published Web services.

The beta version of the API is available from the iPhone Resource Center and includes

• Conceptual and reference help guide
• Integrated templates and documentation
• Community resources, including code galleries, sample applications, forums, and blog

(Source: Esri.com)

Beacon Reference Stations

The Beacon Station List currently contains details of nearly 200 beacon stations throughout the world. Select a Country from the list below, and a State or Province where appropriate, to show information on the location and transmission details of beacon stations in that area.
Trimble provides no guarantee as to the availability or reliability of the data from the beacon stations listed here. Please contact Trimble Support to report any additions or changes to the beacon station list.

Beacon Station Location

		Australia	Latvia
		Belgium	Lithuania
		Bermuda	Malaysia
		Brazil	Netherlands
		Canada	New Zealand
		China	Norway
		Denmark	Panama
		Egypt	Poland
		Estonia	Puerto Rico
		Finland	Russia
		France	Saudi Arabia
		Germany	Singapore
		Hong Kong	South Africa
		Iceland	Spain
		India	Sweden
		Ireland	Taiwan
		Japan	United Arab Emirates
		Korea	United Kingdom
		Kuwait	USA

(Source: http://www.trimble.com)

GIS Training with QGIS - Exercise 5: Using the Field Calculator

1. Load OSM layer
a) From the directory Geodata\vector\OSM load the OSM vector layer.
b) In Settings->Project Properties choose the CRS Pulkovo(1948) EPSG:3330. Verify
that the units are set to meters. Be sure to check the “Enable on the fly” checkbox. Use the
“Zoom Full” button to zoom back to the OSM layer.
2. Edit new polygon layer.
a) Create a new vector polygon layer. Add two attribute columns: FarmerName as text and
AreaSqm as a whole number. Call the new layer Fields, and save in the
Geodata\Fruitfly directory.
b) Start editing the new layer, and digitize four or five new polygon fields on the map. Enter a
farmer's name in the Farmer_Name column for each field. When you're finished, stop
editing.
c) Open the layer's Attribute table and click the Edit button. Now click the Field Calculator
button, to start the Field calculator. Check the Use existing field option and select
the AreaSqm field. Then click the Area button. Stop editing and close the Field
calculator. Examine the results and close the Attribute table.
3. Create a spreadsheet data table.
a) Using Openoffice.org or Excel create a table with two columns: Farmer and Yield. In the
Farmer column enter the exact same names as in the polygon shapefile attribute table. In
the Yield column enter some numeric values.
b) Save the spreadsheet as a dbf file, yields.dbf in the Geodata\Fruitfly directory.
4. Field Calculator
a) Now, back to QGIS, select the menu item Vector->Data Management->Join
Attributes. Select the Fields shapefile as the target, and the FarmerName column as
the target join field. Click the Join dbf table radio button, and browse to select the new
yields.dbf file. Use the Farmer column as the Join field. For the output shapefile, click
browse and enter the name farmer_yields.shp into the Geodata\Fruitfly directory.
After clicking OK answer Yes to add the new shapefile to the map.
b) Select the new farmer_yields layer in the table of contents, and open its attribute table.
c) Begin editing and click the Field Calculator. In the New Field section enter
Yld_per_Ha as the Output field name. Set it's Output field type as Decimal
number.
d) Now using the available fields and the operator buttons, create the following expression in
the lower Field calculator expression window:
( Yield / AreaSqm ) * 10000. Click OK to run the calculation.
5. Display using Graduated symbol.
a) Open the Properties window, Symbology tab, for the farmer_yields layer.
b) Select to display using Graduated symbol. Choose the Yld_per_Ha column as the
Classification field, and choose Number of classes equal to the number of polygons in
your farmer_yields layer. Now click the Classify button, and click OK to examine the
results.

hurricane sandy news

(http://www.nhc.noaa.gov/gtwo_atl.shtml)

Encontro Quantum GIS - 29 e 30 de Outubro 2012

Source (www.qgis.org)

Encontro Quantum GIS, 29 e 30 Outubro 2012

Auditório 6.1.36 – C6, Piso 1, Sala 36 - Faculdade de Ciências da Universidade de Lisboa (Campo Grande)

Um encontro informal acerca do presente e futuro do Quantum GIS (software SIG Open Source), aberto a todos! Direccionado paratécnicos, estudantes, professores e programadores GIS, pretende dar a conhecer as novidades, tendências e casos de estudoPortugueses. Para quem queira "passar à prática", este ano será ainda promovido um dia de workshops temáticos.

Inscrição gratuita, mas obrigatória (lugares limitados)

Inscrições FECHADAS

Para mais informações contacte-nos atraves do endereço E-Mail: info@faunalia.pt

2013 International Forum on Advances in Engineering(IFAE 2013)

March 22-23, 2013. New Delhi, India 

2012-10-7 News: Call for papers(Download)

The 2013 International Forum on Advances in Engineering (IFAE 2013) will be held from March 22~23, 2013 in New Delhi, India. The main objective of the conference is to gather world-class researchers, engineers and educators engaged in the fields of engineering and technology to meet and present their latest activities. It will provide you a platform to dissimilate your research findings, hopefully, it will also spark innovative ideas, foster research relations or partnerships between the various institutions. You are cordially invited to attend this interesting event. We want you to be a part of the global collaboration in the research of engineering and technology.

This conference is sponsored by Computer Science and Electronic Technology International Society, and co-sponsored by Azad University of Quchan, Balaji Institute of Technology & Science, Monash University , Trans tech publications inc. and Scientific.net. Other technical sponsors are also solicited. If your institution would like to be a technical sponsor, please contact the conference secretary (please note, your request does not guarantee selection of being a sponsor of the conference).

All paper submissions for presentation and conference publication will be peer reviewed and evaluated. Selection is based on originality, technical and/or research content/depth, correctness, relevance to conference, contributions, and readability.

All papers for the IFAE 2013 will be published in the International Journal of "Advanced Engineering Forum" (ISSN: 2234-9898) as one volume, and will be indexed by Elsevier: SCOPUS www.scopus.com and Ei Compendex (CPX) www.ei.org/. Cambridge Scientific Abstracts (CSA) www.csa.com, Chemical Abstracts (CA) www.cas.org, Google and Google Scholar google.com, Thomson (Web of Science, CPCI/ISTP) www.isinet.com, Institution of Electrical Engineers (IEE) www.iee.org, etc.

(http://www.csetis.hk)

Tracking Hurricane Sandy in Google Earth

With Hurricane Sandy hitting the Bahamas and heading toward the United States, Google has set up their Crisis Response Map to try to help with the situation. The map includes various tools such as public alerts, emergency shelters and (as pointed out by Google Maps Mania and shown below) wind speed probability charts.

If you're in Google Earth, there are some great tools available to you in there as well. By opening the [Weather] layer, you can turn on near-real-time [Clouds] and [Radar] layers, which show the storm gaining strength:

If you turn on the main [Places] layer in Google Earth, a small hurricane icon will appear in the center of the storm. By clicking the icon you can view news, advisories, as well as three and five day path predictions.

If you come across any other tools that help with the tracking of this storm, leave a comment below and let us know.

India's Biodiversity on Google Maps

 
The India Biodiversity Portal is a participatory platform for creating and sharing biodiversity information for the Indian subcontinent.

The maps section of the India Biodiversity Portal has a collection of more than one hundred interactive map layers that can be viewed on a Google Map. The layers are organised by theme (Biogeography, Abiotic, Demography, Species, Administrative Units, Land Use Land Cover, Conservation) and by geography.

Users can add multiple layers to the map and order the layers as they require.

OpenGeoDa - Free Yourself

My ”learn python because you are a programmer” pissed off a couple people. Look, either embrace change or be replaced. The idea that you’ll sit at some desk, string together ArcGIS Toolbox wizards doesn’t end well. This only results in you getting paid minimum wage with no where to go. The reality of the world we are in is the only thing you have to separate yourself from the 7 billion other people in the world is your flexibility and skills. If you don’t stand out, you’ll be nothing but a chair moistener in sector 7g.

Now that doesn’t mean you can’t use ArcGIS, quite the contrary. It is still one of the best tools to do much GIS. But you need to augment your “Esri skillz” with other toolsets that will give you a leg up when you want to get out of the cul-de-sac.

I had beers with a new friend of mine last Friday and we were talking about how to expand your skillset in ways to benefit your professional growth. Of course I mentioned Python but she already knew that. Python is great because it is not disruptive at all and works well within the Esri silo. The other application I recommended to her was OpenGeoDa from Arizona State University.

GeoDa is a free software program that serves as an introduction to spatial data analysis. OpenGeoDa is the cross-platform, open source version that runs on different versions of Windows (including XP, Vista and 7), Mac OS, and Linux.

What does that bring to the table? Open source, cross-platform spatial data analysis. It is sexy just saying that. With 70,000 users, GeoDa is clearly established and will help you get a better understanding of what actual geospatial analysis is. Wizards only hide learning from you and cause you to be a button pusher. Esri likes this because it allows them to sell more ArcGIS licenses to anyone who can use a mouse, but it won’t make you more valuable.

Of course learning a database, PostGIS, etc can help as well as Brian Timoney points out. But tools such as OpenGeoDa can be integrated into your workflows easily and give you the skills to make yourself much more valuable to organizations. Much like Paul Ryan, you need exercise (in this case you skills, not your biceps) to keep your focus.

My hangout with Nathaniel Kelso was very interesting because he talked about how Stamen was doing amazing visualization work for Facebook and others. That’s the future, not migrating the old way of doing things “to the cloud”. Onwards….

OpenGeoDa - Free Yourself

My ”learn python because you are a programmer” pissed off a couple people. Look, either embrace change or be replaced. The idea that you’ll sit at some desk, string together ArcGIS Toolbox wizards doesn’t end well. This only results in you getting paid minimum wage with no where to go. The reality of the world we are in is the only thing you have to separate yourself from the 7 billion other people in the world is your flexibility and skills. If you don’t stand out, you’ll be nothing but a chair moistener in sector 7g.

Now that doesn’t mean you can’t use ArcGIS, quite the contrary. It is still one of the best tools to do much GIS. But you need to augment your “Esri skillz” with other toolsets that will give you a leg up when you want to get out of the cul-de-sac.

I had beers with a new friend of mine last Friday and we were talking about how to expand your skillset in ways to benefit your professional growth. Of course I mentioned Python but she already knew that. Python is great because it is not disruptive at all and works well within the Esri silo. The other application I recommended to her was OpenGeoDa from Arizona State University.

GeoDa is a free software program that serves as an introduction to spatial data analysis. OpenGeoDa is the cross-platform, open source version that runs on different versions of Windows (including XP, Vista and 7), Mac OS, and Linux.

What does that bring to the table? Open source, cross-platform spatial data analysis. It is sexy just saying that. With 70,000 users, GeoDa is clearly established and will help you get a better understanding of what actual geospatial analysis is. Wizards only hide learning from you and cause you to be a button pusher. Esri likes this because it allows them to sell more ArcGIS licenses to anyone who can use a mouse, but it won’t make you more valuable.

Of course learning a database, PostGIS, etc can help as well as Brian Timoney points out. But tools such as OpenGeoDa can be integrated into your workflows easily and give you the skills to make yourself much more valuable to organizations. Much like Paul Ryan, you need exercise (in this case you skills, not your biceps) to keep your focus.

My hangout with Nathaniel Kelso was very interesting because he talked about how Stamen was doing amazing visualization work for Facebook and others. That’s the future, not migrating the old way of doing things “to the cloud”. Onwards….

Tutorial Oracle Spatial

Résumé

Le présent document est un tutorial pour la gestion des données spatiales des base de données Oracle. Il n'est de loin pas exhaustif, mais il donne un aperçu des possibilités offerers par Oracle spatial et ces concurrents.

lire la suite ...

Writing your first Django app, part 1

Let’s learn by example.

Throughout this tutorial, we’ll walk you through the creation of a basic poll application.

It’ll consist of two parts:

• A public site that lets people view polls and vote in them.
• An admin site that lets you add, change and delete polls.

We’ll assume you have Django installed already. You can tell Django is installed and which version by running the following command:

python -c "import django; print(django.get_version())"

You should see either the version of your Django installation or an error telling "No module named django". Check also that the version number matches the version of this tutorial. If they don't match, you can refer to the tutorial for your version of Django or update Django to the newest version.

See How to install Django for advice on how to remove older versions of Django and install a newer one.

Where to get help:

If you're having trouble going through this tutorial, please post a message to django-users or drop by #django on irc.freenode.net to chat with other Django users who might be able to help.

Creating a project

If this is your first time using Django, you'll have to take care of some initial setup. Namely, you'll need to auto-generate some code that establishes a Django project -- a collection of settings for an instance of Django, including database configuration, Django-specific options and application-specific settings.

From the command line, cd into a directory where you'd like to store your code, then run the following command:

django-admin.py startproject mysite

This will create a mysite directory in your current directory. If it didn't work, see Troubleshooting.

Script name may differ in distribution packages

If you installed Django using a Linux distribution's package manager (e.g. apt-get or yum) django-admin.py may have been renamed to django-admin. You may continue through this documentation by omitting .py from each command.

Mac OS X permissions

If you're using Mac OS X, you may see the message "permission denied" when you try to rundjango-admin.py startproject. This is because, on Unix-based systems like OS X, a file must be marked as "executable" before it can be run as a program. To do this, open Terminal.app and navigate (using the cdcommand) to the directory where django-admin.py is installed, then run the commandsudo chmod +x django-admin.py.

Note

You'll need to avoid naming projects after built-in Python or Django components. In particular, this means you should avoid using names like django (which will conflict with Django itself) or test (which conflicts with a built-in Python package).

Where should this code live?

If your background is in PHP, you're probably used to putting code under the Web server's document root (in a place such as /var/www). With Django, you don't do that. It's not a good idea to put any of this Python code within your Web server's document root, because it risks the possibility that people may be able to view your code over the Web. That's not good for security.

Put your code in some directory outside of the document root, such as /home/mycode.

Let's look at what startproject created:

mysite/
    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        wsgi.py

Doesn't match what you see?

The default project layout recently changed. If you're seeing a "flat" layout (with no inner mysite/ directory), you're probably using a version of Django that doesn't match this tutorial version. You'll want to either switch to the older tutorial or the newer Django version.

These files are:

• The outer mysite/ directory is just a container for your project. Its name doesn't matter to Django; you can rename it to anything you like.
• manage.py: A command-line utility that lets you interact with this Django project in various ways. You can read all the details about manage.py in django-admin.py and manage.py.
• The inner mysite/ directory is the actual Python package for your project. Its name is the Python package name you'll need to use to import anything inside it (e.g. import mysite.settings).
• mysite/__init__.py: An empty file that tells Python that this directory should be considered a Python package. (Readmore about packages in the official Python docs if you're a Python beginner.)
• mysite/settings.py: Settings/configuration for this Django project. Django settings will tell you all about how settings work.
• mysite/urls.py: The URL declarations for this Django project; a "table of contents" of your Django-powered site. You can read more about URLs in URL dispatcher.
• mysite/wsgi.py: An entry-point for WSGI-compatible webservers to serve your project. See How to deploy with WSGI for more details.

The development server

Let's verify this worked. Change into the outer mysite directory, if you haven't already, and run the commandpython manage.py runserver. You'll see the following output on the command line:

Validating models...
0 errors found.

Django version 1.4, using settings 'mysite.settings'
Development server is running at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

You've started the Django development server, a lightweight Web server written purely in Python. We've included this with Django so you can develop things rapidly, without having to deal with configuring a production server -- such as Apache -- until you're ready for production.

Now's a good time to note: DON'T use this server in anything resembling a production environment. It's intended only for use while developing. (We're in the business of making Web frameworks, not Web servers.)

Now that the server's running, visit http://127.0.0.1:8000/ with your Web browser. You'll see a "Welcome to Django" page, in pleasant, light-blue pastel. It worked!

Changing the port

By default, the runserver command starts the development server on the internal IP at port 8000.

If you want to change the server's port, pass it as a command-line argument. For instance, this command starts the server on port 8080:

python manage.py runserver 8080

If you want to change the server's IP, pass it along with the port. So to listen on all public IPs (useful if you want to show off your work on other computers), use:

python manage.py runserver 0.0.0.0:8000

Full docs for the development server can be found in the runserver reference.

Database setup

Now, edit mysite/settings.py. It's a normal Python module with module-level variables representing Django settings. Change the following keys in the DATABASES 'default' item to match your database connection settings.

• ENGINE -- Either 'django.db.backends.postgresql_psycopg2', 'django.db.backends.mysql','django.db.backends.sqlite3' or 'django.db.backends.oracle'. Other backends are also available.
• NAME -- The name of your database. If you're using SQLite, the database will be a file on your computer; in that case, NAMEshould be the full absolute path, including filename, of that file. If the file doesn't exist, it will automatically be created when you synchronize the database for the first time (see below).
  When specifying the path, always use forward slashes, even on Windows (e.g. C:/homes/user/mysite/sqlite3.db).
• USER -- Your database username (not used for SQLite).
• PASSWORD -- Your database password (not used for SQLite).
• HOST -- The host your database is on. Leave this as an empty string if your database server is on the same physical machine (not used for SQLite).

If you're new to databases, we recommend simply using SQLite by setting ENGINE to 'django.db.backends.sqlite3' and NAMEto the place where you'd like to store the database. SQLite is included in Python, so you won't need to install anything else to support your database.

Note

If you're using PostgreSQL or MySQL, make sure you've created a database by this point. Do that with "CREATE DATABASE database_name;" within your database's interactive prompt.

If you're using SQLite, you don't need to create anything beforehand - the database file will be created automatically when it is needed.

While you're editing settings.py, set TIME_ZONE to your time zone. The default value is the Central time zone in the U.S. (Chicago).

Also, note the INSTALLED_APPS setting toward the bottom of the file. That holds the names of all Django applications that are activated in this Django instance. Apps can be used in multiple projects, and you can package and distribute them for use by others in their projects.

By default, INSTALLED_APPS contains the following apps, all of which come with Django:

• django.contrib.auth -- An authentication system.
• django.contrib.contenttypes -- A framework for content types.
• django.contrib.sessions -- A session framework.
• django.contrib.sites -- A framework for managing multiple sites with one Django installation.
• django.contrib.messages -- A messaging framework.
• django.contrib.staticfiles -- A framework for managing static files.

These applications are included by default as a convenience for the common case.

Each of these applications makes use of at least one database table, though, so we need to create the tables in the database before we can use them. To do that, run the following command:

python manage.py syncdb

The syncdb command looks at the INSTALLED_APPS setting and creates any necessary database tables according to the database settings in your settings.py file. You'll see a message for each database table it creates, and you'll get a prompt asking you if you'd like to create a superuser account for the authentication system. Go ahead and do that.

If you're interested, run the command-line client for your database and type \dt (PostgreSQL), SHOW TABLES; (MySQL), or.schema (SQLite) to display the tables Django created.

For the minimalists

Like we said above, the default applications are included for the common case, but not everybody needs them. If you don't need any or all of them, feel free to comment-out or delete the appropriate line(s) from INSTALLED_APPSbefore running syncdb. The syncdb command will only create tables for apps in INSTALLED_APPS.

Creating models

Now that your environment -- a "project" -- is set up, you're set to start doing work.

Each application you write in Django consists of a Python package, somewhere on your Python path, that follows a certain convention. Django comes with a utility that automatically generates the basic directory structure of an app, so you can focus on writing code rather than creating directories.

Projects vs. apps

What's the difference between a project and an app? An app is a Web application that does something -- e.g., a Weblog system, a database of public records or a simple poll app. A project is a collection of configuration and apps for a particular Web site. A project can contain multiple apps. An app can be in multiple projects.

Your apps can live anywhere on your Python path. In this tutorial, we'll create our poll app right next to your manage.py file so that it can be imported as its own top-level module, rather than a submodule of mysite.

To create your app, make sure you're in the same directory as manage.py and type this command:

python manage.py startapp polls

That'll create a directory polls, which is laid out like this:

polls/
    __init__.py
    models.py
    tests.py
    views.py

This directory structure will house the poll application.

The first step in writing a database Web app in Django is to define your models -- essentially, your database layout, with additional metadata.

Philosophy

A model is the single, definitive source of data about your data. It contains the essential fields and behaviors of the data you're storing. Django follows the DRY Principle. The goal is to define your data model in one place and automatically derive things from it.

In our simple poll app, we'll create two models: Poll and Choice. A Poll has a question and a publication date. A Choice has two fields: the text of the choice and a vote tally. Each Choice is associated with a Poll.

These concepts are represented by simple Python classes. Edit the polls/models.py file so it looks like this:

from django.db import models

class Poll(models.Model):
    question = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField()

The code is straightforward. Each model is represented by a class that subclasses django.db.models.Model. Each model has a number of class variables, each of which represents a database field in the model.

Each field is represented by an instance of a Field class -- e.g., CharField for character fields and DateTimeField for datetimes. This tells Django what type of data each field holds.

The name of each Field instance (e.g. question or pub_date ) is the field's name, in machine-friendly format. You'll use this value in your Python code, and your database will use it as the column name.

You can use an optional first positional argument to a Field to designate a human-readable name. That's used in a couple of introspective parts of Django, and it doubles as documentation. If this field isn't provided, Django will use the machine-readable name. In this example, we've only defined a human-readable name for Poll.pub_date. For all other fields in this model, the field's machine-readable name will suffice as its human-readable name.

Some Field classes have required elements. CharField, for example, requires that you give it a max_length. That's used not only in the database schema, but in validation, as we'll soon see.

Finally, note a relationship is defined, using ForeignKey. That tells Django each Choice is related to a single Poll. Django supports all the common database relationships: many-to-ones, many-to-manys and one-to-ones.

Activating models

That small bit of model code gives Django a lot of information. With it, Django is able to:

• Create a database schema (CREATE TABLE statements) for this app.
• Create a Python database-access API for accessing Poll and Choice objects.

But first we need to tell our project that the polls app is installed.

Philosophy

Django apps are "pluggable": You can use an app in multiple projects, and you can distribute apps, because they don't have to be tied to a given Django installation.

Edit the settings.py file again, and change the INSTALLED_APPS setting to include the string 'polls'. So it'll look like this:

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    # Uncomment the next line to enable the admin:
    # 'django.contrib.admin',
    # Uncomment the next line to enable admin documentation:
    # 'django.contrib.admindocs',
    'polls',
)

Now Django knows to include the polls app. Let's run another command:

python manage.py sql polls

You should see something similar to the following (the CREATE TABLE SQL statements for the polls app):

BEGIN;
CREATE TABLE "polls_poll" (
    "id" serial NOT NULL PRIMARY KEY,
    "question" varchar(200) NOT NULL,
    "pub_date" timestamp with time zone NOT NULL
);
CREATE TABLE "polls_choice" (
    "id" serial NOT NULL PRIMARY KEY,
    "poll_id" integer NOT NULL REFERENCES "polls_poll" ("id") DEFERRABLE INITIALLY DEFERRED,
    "choice_text" varchar(200) NOT NULL,
    "votes" integer NOT NULL
);
COMMIT;

Note the following:

• The exact output will vary depending on the database you are using.
• Table names are automatically generated by combining the name of the app (polls) and the lowercase name of the model -- poll and choice. (You can override this behavior.)
• Primary keys (IDs) are added automatically. (You can override this, too.)
• By convention, Django appends "_id" to the foreign key field name. (Yes, you can override this, as well.)
• The foreign key relationship is made explicit by a REFERENCES statement.
• It's tailored to the database you're using, so database-specific field types such as auto_increment (MySQL), serial(PostgreSQL), or integer primary key (SQLite) are handled for you automatically. Same goes for quoting of field names -- e.g., using double quotes or single quotes. The author of this tutorial runs PostgreSQL, so the example output is in PostgreSQL syntax.
• The sql command doesn't actually run the SQL in your database - it just prints it to the screen so that you can see what SQL Django thinks is required. If you wanted to, you could copy and paste this SQL into your database prompt. However, as we will see shortly, Django provides an easier way of committing the SQL to the database.

If you're interested, also run the following commands:

• python manage.py validate -- Checks for any errors in the construction of your models.
• python manage.py sqlcustom polls -- Outputs any custom SQL statements (such as table modifications or constraints) that are defined for the application.
• python manage.py sqlclear polls -- Outputs the necessary DROP TABLE statements for this app, according to which tables already exist in your database (if any).
• python manage.py sqlindexes polls -- Outputs the CREATE INDEX statements for this app.
• python manage.py sqlall polls -- A combination of all the SQL from the sql, sqlcustom, and sqlindexes commands.

Looking at the output of those commands can help you understand what's actually happening under the hood.

Now, run syncdb again to create those model tables in your database:

python manage.py syncdb

The syncdb command runs the SQL from sqlall on your database for all apps in INSTALLED_APPS that don't already exist in your database. This creates all the tables, initial data and indexes for any apps you've added to your project since the last time you ran syncdb. syncdb can be called as often as you like, and it will only ever create the tables that don't exist.

Read the django-admin.py documentation for full information on what the manage.py utility can do.

Playing with the API

Now, let's hop into the interactive Python shell and play around with the free API Django gives you. To invoke the Python shell, use this command:

python manage.py shell

We're using this instead of simply typing "python", because manage.py sets the DJANGO_SETTINGS_MODULE environment variable, which gives Django the Python import path to your settings.py file.

Bypassing manage.py

If you'd rather not use manage.py, no problem. Just set the DJANGO_SETTINGS_MODULE environment variable tomysite.settings and run python from the same directory manage.py is in (or ensure that directory is on the Python path, so that import mysite works).

For more information on all of this, see the django-admin.py documentation.

Once you're in the shell, explore the database API:

>>> from polls.models import Poll, Choice   # Import the model classes we just wrote.

# No polls are in the system yet.
>>> Poll.objects.all()
[]

# Create a new Poll.
# Support for time zones is enabled in the default settings file, so
# Django expects a datetime with tzinfo for pub_date. Use timezone.now()
# instead of datetime.datetime.now() and it will do the right thing.
>>> from django.utils import timezone
>>> p = Poll(question="What's new?", pub_date=timezone.now())

# Save the object into the database. You have to call save() explicitly.
>>> p.save()

# Now it has an ID. Note that this might say "1L" instead of "1", depending
# on which database you're using. That's no biggie; it just means your
# database backend prefers to return integers as Python long integer
# objects.
>>> p.id
1

# Access database columns via Python attributes.
>>> p.question
"What's new?"
>>> p.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)

# Change values by changing the attributes, then calling save().
>>> p.question = "What's up?"
>>> p.save()

# objects.all() displays all the polls in the database.
>>> Poll.objects.all()
[<Poll: Poll object>]

Wait a minute. <Poll: Poll object> is, utterly, an unhelpful representation of this object. Let's fix that by editing the polls model (in the polls/models.py file) and adding a __unicode__() method to both Poll and Choice:

class Poll(models.Model):
    # ...
    def __unicode__(self):
        return self.question

class Choice(models.Model):
    # ...
    def __unicode__(self):
        return self.choice_text

It's important to add __unicode__() methods to your models, not only for your own sanity when dealing with the interactive prompt, but also because objects' representations are used throughout Django's automatically-generated admin.

Why __unicode__() and not __str__()?

If you're familiar with Python, you might be in the habit of adding __str__() methods to your classes, not__unicode__() methods. We use __unicode__() here because Django models deal with Unicode by default. All data stored in your database is converted to Unicode when it's returned.

Django models have a default __str__() method that calls __unicode__() and converts the result to a UTF-8 bytestring. This means that unicode(p) will return a Unicode string, and str(p) will return a normal string, with characters encoded as UTF-8.

If all of this is gibberish to you, just remember to add __unicode__() methods to your models. With any luck, things should Just Work for you.

Note these are normal Python methods. Let's add a custom method, just for demonstration:

import datetime
from django.utils import timezone
# ...
class Poll(models.Model):
    # ...
    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

Note the addition of import datetime and from django.utils import timezone, to reference Python's standard datetimemodule and Django's time-zone-related utilities in django.utils.timezone, respectively. If you aren't familiar with time zone handling in Python, you can learn more in the time zone support docs.

Save these changes and start a new Python interactive shell by running python manage.py shell again:

>>> from polls.models import Poll, Choice

# Make sure our __unicode__() addition worked.
>>> Poll.objects.all()
[<Poll: What's up?>]

# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
>>> Poll.objects.filter(id=1)
[<Poll: What's up?>]
>>> Poll.objects.filter(question__startswith='What')
[<Poll: What's up?>]

# Get the poll whose year is 2012.
>>> Poll.objects.get(pub_date__year=2012)
<Poll: What's up?>

>>> Poll.objects.get(id=2)
Traceback (most recent call last):
    ...
DoesNotExist: Poll matching query does not exist. Lookup parameters were {'id': 2}

# Lookup by a primary key is the most common case, so Django provides a
# shortcut for primary-key exact lookups.
# The following is identical to Poll.objects.get(id=1).
>>> Poll.objects.get(pk=1)
<Poll: What's up?>

# Make sure our custom method worked.
>>> p = Poll.objects.get(pk=1)
>>> p.was_published_recently()
True

# Give the Poll a couple of Choices. The create call constructs a new
# Choice object, does the INSERT statement, adds the choice to the set
# of available choices and returns the new Choice object. Django creates
# a set to hold the "other side" of a ForeignKey relation
# (e.g. a poll's choices) which can be accessed via the API.
>>> p = Poll.objects.get(pk=1)

# Display any choices from the related object set -- none so far.
>>> p.choice_set.all()
[]

# Create three choices.
>>> p.choice_set.create(choice_text='Not much', votes=0)
<Choice: Not much>
>>> p.choice_set.create(choice_text='The sky', votes=0)
<Choice: The sky>
>>> c = p.choice_set.create(choice_text='Just hacking again', votes=0)

# Choice objects have API access to their related Poll objects.
>>> c.poll
<Poll: What's up?>

# And vice versa: Poll objects get access to Choice objects.
>>> p.choice_set.all()
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> p.choice_set.count()
3

# The API automatically follows relationships as far as you need.
# Use double underscores to separate relationships.
# This works as many levels deep as you want; there's no limit.
# Find all Choices for any poll whose pub_date is in 2012.
>>> Choice.objects.filter(poll__pub_date__year=2012)
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]

# Let's delete one of the choices. Use delete() for that.
>>> c = p.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()