building an online tool for spatial joins using open source software karsten vennemann seattle

Building an online tool for spatial joins

using open source software

Karsten Vennemann

Seattle


- - - - Why this tool ? What does it do ?

- - - - Steps to retrieve results

- - - - Tool live demo

- - - - How does it work ?

- - - - How can you build your own ?

Talk Overview

• Who, Why and What

• Tool Workflow

• Definitions and Examples

• Technical Background

• Resources


Why this online tool ? Why open source software ?Finding the Legal District in which a member of an organization lives is important information for many environmental voter advocacy groups. While this easily can be accomplished using commercial GIS tools, most of those Non-Profit organizations lack the resources and/or technical staff to support the use of such software.

Adding Legislative District information is usually done manually.In Washington State there is the online district finder tool available: http://apps.leg.wa.gov/DistrictFinder/Default.aspx

Can find single addresses

Who, Why and What


About this tool

• Windows and Linux server platforms

• based on open source software

• any type of spatial join based on street address in WA state (US) and a polygon layer

For simplicity we will focus on a technical overview onhow a web based tool can allow users with little or no GIS knowledge to attach legislative district information for Washington State to their membership lists.

Who, Why and What


Workflow for the tool can be broken up into four main parts

1) File upload to the server(text or Excel file containing address list via web interface )

2) Geocoding - Retrieval of coordinates (latitude/longitude) for the address (geocoded using 2006 Tiger line data, PHP and Perl)

3) Spatial Join - Matching the Legislative District information(Query onto a PostGIS Database)

4) Transfer result information(streaming the results to the client computer text or MS Excel file)

Tool Workflow


Workflow for the tool can be broken up into four main parts

1) File upload to the server(text or Excel file via web interface )

2) Geocoding - Retrieval of coordinates (latitude/longitude) for the address (geocoded using 2006 Tiger line data, PHP and Perl)

3) Spatial Join - Matching the Legislative District information(Query onto a PostGIS Database)

4) Transfer result information(streaming the results to the client computer text or MS Excel file)

Tool Workflow


What is Geocoding ?

Interpolation of real world coordinates for a given location

Most geocoders use address information to interpolate (estimate) the real world position along streets using blocks and intersections as landmarks

Variety of free tools available - most popular:Google and Yahoo maps API, geocoder.usAlso Tiger line geocoder for Post GIS

=> Geocoder::US a Perl moduleOpen sourcecan download source code and install on your own serveruses Berkeley DB format to store Tiger data- high compression fro data - whole US Street data 750 MB (24 GB of uncompressed Tiger data)

Definitions and Examples


What is a Spatial Join ?A spatial join operation adds information based on the geographical location of one feature to another

ID precinct

352 BEL 48-2776



Spatial JoinA spatial join operation adds information based on the geographical location of one feature to another

ID address

223428

16089 Northrup Way

ID precinct

352 BEL 48-2776



Spatial JoinA spatial join operation adds information based on the geographical location of one feature to another

ID address

223428

16089 Northrup Way

ID precinct

352 BEL 48-2776

ID address precinct

223428

16089 Northrup Way BEL 48-2776



Spatial Join



Live Tool Demo



TechnicalOverview

ServerSide

Apache II

`

ClientSide

wwwhttp

BrowserHTML Form

PHP

php_perlphp_pgsql

Perl

Geo::Coder::USSQL

Upload Directory:membership file

Berkeley DB

2006 Tiger Line Data WA State

PostGIS DB

spatial layer Legal Districts WA

upload filestream results

text or Excel file

Technical Background


Technical Overview

1. Text or Excel file is read with php2. Get user input to select address fields3. Address is concatenated and feed into the geocoder::US Perl module

from within php4. lat/long returned 5. Spatial query using lat/long results from geocoding

=> in Post GIS one simple SQL query is called to retrieve the LD number

6. Output of results

Sample sql queries

select ndistrict from Leg_districts_2001 where Leg_districts_2001.the_geom && (setsrid((MakePoint(-122.206834, 47.611421)),4326)) and intersects (Leg_districts_2001.the_geom,setsrid((MakePoint(-122.206834, 47.611421)),4326));

select ndistrict from Leg_districts_2001 where Leg_districts_2001.the_geom && transform(((setsrid((MakePoint(-122.206834, 47.611421)),4326))),2285) and intersects (Leg_districts_2001.the_geom,transform(((setsrid((MakePoint(-122.206834, 47.611421)),4326))),2285));



Code



Perl integration for Geo::Coder::US



Query in PostGIS



Source: “Introduction to PostGIS”, Paul Ramsey, Refractions Research

Spatial Indexes


How can you build your own tool ?

Install

• Apache I or II Webserver (or IIS)

• PHP (php_Perl.dll, php_pgsql.dll etc.)

• Perl (5.8 or higher, geocoder::US module and several others from CPAN)

• PostgreSQL

• PostGIS, load polygon data

• Obtain US Census Tiger Line data for states in question

• Load Tiger data into BerkeleyDB (utility comes with Geo::Coder::US)

• author some PHP/Perl scripts



Open source utilities and websites

Geocoder scripts http://geocoder.us

Census Tiger Line files

http://www.census.gov/geo/www/tiger/

PHP http://www.php.net/downloads.php

Perl (Active State) http://www.activestate.com/Products/ActivePerl

php_perl Extension http://devzone.zend.com/node/view/id/1712

PostgreSQL http://www.postgresql.org

PostGIS http://postgis.refractions.net

BerkeleyDB http://www.oracle.com/database/berkeley-db/index.html

Resources

http://geocoder.us/

http://geocoder.us/


Articles

Build Your Own Geocoding Solution with Geo::Coder::USBy Jason Gilmorehttp://www.developer.com/tech/article.php/3557171

Retrieving Map Location CoordinatesBy Jason Gilmorehttp://www.developer.com/tech/article.php/3548171

Resources


Free and Open Source Software for Geospatial 2007

http://www.foss4g2007.org/Resources


New local GIS user group:

“Cascadia Users of Geospatial Open Source”

http://groups.google.com/group/cugos

Next meeting today April 25th, 5:30 pmIn the LizardTech offices, located near Pioneer Square:

The National BuildingSuite 2001008 Western AvenueSeattle, WA 98104

Resources

http://groups.google.com/group/cugos

building an online tool for spatial joins using open source software karsten vennemann seattle

Documents

online tool

tool windows

tool workflow definitions

web based tool

spatial joins workflow

tool live demo

address information

type of spatial join