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title: Open-source Geospatial Web Stack Workshop class: animation-fade layout: true

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{{title}}, Day 1

July 12, GIS Education Center, Galvanize

Introductions

Who am I?

Rob Gaston

  • Geospatial web application developer, Farallon Geographics (10 years)

  • Sometime educator, GIS Education Center & General Assembly

  • Cat lover, volunteer and foster with Cat Town, Oakland

--

Who are you?

...and what do you hope to get from this workshop?

This workshop will be:

A practical introduction to a powerful stack of free, open-source web tools for geospatial web development.

We're going to focus on a hands-on approach to learning the basics of:

  • PostgreSQL/PostGIS (spatially-enabled RDBMS)

  • GeoServer (Geospatial data server)

  • Leaflet (JavaScript mapping library)

This workshop won't be:

A thorough academic explanation of GIS or related concepts. We're not going to spend a lot of time talking about the basics of:

  • GIS

  • RDBMS/SQL

  • JavaScript

  • HTML/CSS

...but we're going to try to keep things simple and easy, so don't worry if you're not an expert - some basic comfort and confidence will suffice.

We're also going to focus solely on a developer environment - we simply won't have time to talk about production/cloud deployment.

As we're working...

  • these slides are viewable at http://rgaston.com/osgw/

  • you are encouraged to follow along on your laptop

  • there are helpful links throughout that you may want to reference during the exercise

  • but, please, try not to jump ahead

  • please refrain from starting on the hands-on exercises until I come to those slides or working on the exercises while we're talking

  • if you finish a particular exercise and others are still working, find a student who is still working to help (it's really the best way to learn and build confidence)

  • be nice to each other!

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Part 1: PostgreSQL & PostGIS basics

What is PostgreSQL?

PostgreSQL is a free and open-source relational database management system (RDBMS), first released in 1996. It is powerful, secure and fully featured while also being easy to install and administer.

--

Other popular RDBMS's include:

  • MySQL (also open-source)

  • Oracle

  • Microsoft SQL Server

--

RDBMS's provide for the management of relational data tables through the use of foreign key relationships.

Advantages over flat-files beyond a relational model include scalability and security.

The language for querying RDBMS's is called Structured Query Language (SQL).

What is PostGIS?

PostGIS is the geospatial extension for PostgreSQL, it provides:

--

  • ability to store geospatial data in tables using the "geometry" data type

    • high degree of flexibility here as compared to shapefiles

    • a single geometry column can store geometries of many types ([multi-]points, lines, or polygons).

    • geometries stored in the same column should use the same spatial reference system

--

  • lots of functions for working with geospatial data, including:

    • transformation (such as between different spatial reference systems)

    • output formatting

    • spatial querying

Installing PostgreSQL

PostgreSQL installation can be tricky, as there are many paths. For this workshop we will use:

We'll be using these tools because:

  1. they are easy to install

  2. they include the PostGIS extension, so we won't have to install it separately.

Don't rush out and install these right this second - we're going to do that in just a minute.

Working with PostgreSQL

There are lots of tools for working with PostgreSQL and PostGIS. The most common are:

  • the GUI client, PgAdmin4

    • shows a nice tree view of database entities

    • simple tools for querying data using SQL.

    • it is what we will be using during this workshop.

  • the command line client, psql (it comes with PostgreSQL)

    • allows execution of SQL against PostgreSQL databases from a command line

  • the GIS client, QGIS

    • does a lot more than just PostGIS, but they go together well

Creating a spatially-enabled database (part 1)

To create a spatially-enabled database in PostgreSQL using PgAdmin4:

  • if you haven't, create a connection to your local PostgreSQL instance

    • give your connection a "Name" on the "General" tab (something like "localhost")

    • specify the "Host name/adress" as "localhost" on the "Connection" tab

  • right-click on the connection name and select "Create" > "Database"

    • give your database a name (for example, "osgw") and hit "Save"

Creating a spatially-enabled database (part 2)

To enable PostGIS on your database:

  • right-click on your database's name in the tree view on the left and select "Query Tool"

  • paste the following SQL into the resulting SQL query window, and press the lightning bolt button or f5 to run it:

-- Enable PostGIS (includes raster)
CREATE EXTENSION postgis;
-- Enable Topology
CREATE EXTENSION postgis_topology;
  • you can verify that PostGIS is enabled on your database by running the following SQL:
SELECT postgis_version();

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Demo: Creating a spatially-enabled database with PgAdmin4

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Hands-on Exercise

Ex. 1: PostgreSQL & PostGIS setup

On your laptop, please do the following:

  1. install PostgreSQL 9.6 with PostGIS 2 (and command line tools)

  2. install PgAdmin4 (on Windows, you should be able to do this within the Stackbuilder)

  3. using PgAdmin4:

    1. create a new database

    2. add the PostGIS extension to your database

    3. confirm PostGIS is enabled on your database

  4. (optional) install QGIS if you want to quickly visualize your PostGIS tables on a map

  5. extra credit: if you finish early (or already have these installed), find someone who is still working and help them along

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10 minute break

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Part 2: Loading and querying geospatial data with PostGIS

Loading geospatial data into PostgreSQL

  • Geospatial source data are often passed around using the shapefile format.

  • PostGIS provides a command line tool for creating a table from a source shapefile called shp2pgsql

    • shp2pgsql generates the SQL necessary to load your shapefile into a PostgreSQL table

    • usage (reference):

      shp2pgsql -I -s <SRID> <PATH/TO/SHAPEFILE> <SCHEMA>.<DBTABLE> | psql -U postgres -d <DBNAME>

    • for example: given a shapefile, ~/Downloads/states/states.shp, I could load it into a new a table called states in my database osgw like so:

      shp2pgsql -I -s 4326 ~/Downloads/states/states.shp public.states | psql -U postgres -d osgw

Querying data with PgAdmin4

  • With PgAdmin4, you can view the rows in a table either by:

    1. right clicking on your table in the tree view and selecting "View Data" > "View All Rows"

    2. creating a new query with the following SQL (using the name of your table):

      select * from public.states; --

  • Unfortunately, there is no "map" view currently available in PgAdmin4

  • Geometry values shown in PgAdmin4 are not human-readable; however, they can be recast using PostGIS functions...

Using PostGIS geospatial functions

  • PostGIS functions are a powerful set of tools for working with geospatial data

  • They can be called directly in your SQL queries

--

  • For example, you can recast geometries in a select to a more human-readable WKT format like so:

    select *, st_astext(geom) as wkt from public.states;

--

  • as mentioned, PostGIS functions allow for lots of geospatial operations, such as

    • transformation (for example, buffering, or transforming between spatial reference systems)

    • output formatting (as done in the above example with st_astext)

    • spatial querying (for example, joining data from multiple tables with a spatial intersection)

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Demo: Adding a shapefile to PostgreSQL and querying with PostGIS

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Hands-on Exercise

Ex. 2: Loading and querying Geospatial data with PostGIS

  1. download the countries and places shapefiles from Natural Earth

  2. using shp2pgsql, load these two shapefiles into PostgreSQL

  3. using PgAdmin4:

    1. select * from your table to view the data that you just loaded

    2. write a SQL query to join places to countries using a spatial intersection to get a count of place points in each country, hint: you'll need to use a join and a group by in your query. I'll let you figure out which PostGIS function tells you if a polygon contains a point.

  4. extra credit: how else might we use PostGIS spatial processing functions to ask questions about these data? Come up with a question to ask about these data (or others) through spatial processing, find the right PostGIS functions (I can help you) and write a SQL query to get your answer

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10 minute break

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Part 3: Intro to GeoServer

What is GeoServer?

GeoServer is an open source tool for serving up geospatial data that:

  • allows you to create and style "layers" that are served up using open standards for serving raster or vector data

  • will connect to many different data sources, such as:

    • PostGIS

    • Shapefiles

    • Oracle*

    • MySQL*

    • ArcSDE*

** requires installing an extension for GeoServer*

Why do I need services using open standards?

  • Using open standards means that GeoServer services can be consumed by many different clients, from traditional desktop GIS to web applications

  • There are lots of web-based mapping tools that will consume the open standards used by GeoServer, such as:

Installing, running and configuring GeoServer

  • To install GeoServer, get the correct installer for your OS here

  • After installing, you will need to open the application and start the server

  • Once the server is started, you can configure GeoServer using the built in web interface:

    • you can access the web interface by going to: http://localhost:8080/geoserver/web/

    • you'll need to login to administer the server; the default username is "admin" and the default password is "geoserver"

    • in a production environment, you would always want to change the default admin password before going live to the world.

Adding layers to GeoServer

  • Before you can add layers, you will need to connect your data source as a new "Data Store"

    • Go to "Stores" > "Add a new Store" and follow the instructions for your data source type

    • Once added, you will see a list of layers available on the Data Store and an option to publish

  • Each layer that you want to serve up must be published and configured using the "Add Layer" page

    • you must generate a "Native Bounding Box" and "Lat/Lon Bounding Box" before you can publish a layer, which should generally be done from the data itself for the best performance

    • you can select styles to apply to your layer from "Publishing" tab of the "Add Layer" page

  • Once added, you can preview the layer from "Layer Preview" section

  • Layer styles use the StyledLayerDescriptor standard, new styles can be added from the "Styles" section (you can use the Geoserver SLD cookbook as a guide)

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Demo: Starting GeoServer and creating a layer from a shapefile

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Hands-on Exercise

Ex. 3: GeoServer install and basic configuration

On your laptop, do the following:

  1. install GeoServer 2.11.1

  2. start GeoServer

  3. confirm that the server is running by accessing the web interface

  4. using the GeoServer web interface:

    1. create a layer using the countries shapefile

    2. preview your countries shapefile layer

  5. extra credit 1: create a new style in GeoServer for your countries layer, and edit it to use that style

  6. extra credit 2: find another shapefile that interests you, publish it as a layer and create a new style to render you layer in an interesting way.

Homework:

In the time between now and Day 2 of the workshop (July 31), please do the following:

  1. find a shapefile containing data that you would like to load into PostgreSQL/GeoServer

  2. load your shapefile into a PostgreSQL table

  3. create a layer in GeoServer using your shapefile (we're going to get into connecting to PostgreSQL next time)

  4. restyle your layer using the GeoServer web interface

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Thanks - see you on July 31!

...next time: connecting GeoServer to PostgreSQL and viewing data in your own web map...

day 2 slides