Geocoding Web Service

Example

Nancy Read

Metropolitan MosquitoControl District

What is Geocoding?

Address string Location coordinates

2099 University Ave. W 44.959665 °

St. Paul, MN 55104 -93.187222 °

Coordinates used to put point on map:

How we started . . .

MMCD web map site

Address look-up

• Searches Parcels• Gives Choices

Problems

Engine, method – Spelling or order errors (“West 5th” vs “5th West”)

Data – Some parcels not addressed

Maintenance – Load and process updates of parcel layer

Identified Need

Robust geocoding engine Usable with web site (service) Cascading data sets

– address points (when available)– parcels– streets (interpolation)

Host for service, data Data maintenance plan

Internal resources available?

MMCD’s IT Department(note ½ people!)

Need to contract out

Who else has need? solution?

Who needs a Geocoder?

Web map applications– Map Quest– Local Government– King Maps

Other applications– Public Safety

Batch– State Government– Businesses

Find others with need, skills, interest

Dave Bitner (MAC) Jim Maxwell (TLG) Mark Kotz (Met.Co.) Gordy Chinander (MESB) Bob Basquez (St. Paul) Chris Cialek & Jim Dickerson (LMIC) Kent Treichel (MN Dept. of Revenue) Nancy Read (MMCD)- Project Manager

Find resources

Data– Managers of streets, parcels involved

Hosting– MN Land Management Info. Center (LMIC)

Engine, web service– Possible MetroGIS project funding

MetroGIS Geocoder Project

Identified need Applied for MetroGIS project funding,

received $14,000 Defined requirements RFP

Existing Geocoding Services

Proprietary ($$)– ESRI – Envinsa– PxPoint Online

Open Source– Geocoder.us – uses Tiger data

http://geocoder.us/demo.cgi?address=2099+University+Ave.+W.%2C+St.+Paul%2C+MN+55104

PAGC Geocoder engine

Used on large research tasks (e.g, geocoding all fast food retailers in Canada)

Matching routines very good, better than others commonly available “Handles the tough ones others can’t, doesn’t

cascade too quickly to general layers like postal code”

Can handle problems with street ranges

PAGC geocoding engine

Address Matching Algorithms

Match addresses with reference address-ranged street network shapefile

Starts with a rule-based Aho-Corasick driven standardization of both data sources.

Reference data indexed using – BerkeleyDB b-trees for exact key lookups and soundex lookups– pointerless trie indexing scheme for edit distance lookups, adapted

from ideas of Shang and Merrett. Match data records using standard Fellegi-Sunter method with

modifications to permit similarity measures.

PAGC Geocoding engine

Written in ANSI C Open Source, freely distributable

(LGPL – Lesser General Public License) Has supporting web site, documentation and

community, see www.pagcgeo.org Can be used on different resource data files

(not just Tiger or proprietary)

MetroGIS Geocoder Project

Rework PAGC from command line to Service– Pre-process resource street or other

data files to build index files with standardized addresses, location data

– Handle concurrent requests– Run under Apache, on Linux or Windows– Input – Urlencode – Output - XML, JSON, CSV

MetroGIS Geocoder Project

Use applicable standards for parameter names, structures– OGC’s OpenLS Location Utility Service

specification, supported by ArcWeb and Oracle (XML-based)

– FGDC Street Address Data Standard for structuring data (note: “splits” more than OpenLS)

MetroGIS Geocoder Project

Geocoder engine returns location:– Latitude / Longitude– Decimal Degrees

Conversion to UTM or state plane etc. to be done by downstream utility

Capabilities

Cascading (points, parcels, streets)

Geocode to Intersections – will be part of this project– e.g., “University&Snelling”

Not included, to be added later: Landmarks Reverse Geocoding (Location Address)

MetroGIS Geocoder Project

Set up service with Metro data– TLG Streets– 7-county Parcel Layer (centroids)– Address Points (as available)

Host – LMIC – TLG– Can also install locally – need to pre-process data

Expect demo by April 1

Testing planned

Engine– Accuracy and hit rate– Performance and speed– Reliability as web service

Hosting– Ease of set-up

Data– Maintenance

Challenges

Legal agreements – funding– licensing (engine, data)

Code maintenance – Open Source may help Possible hosting issues if service is popular