Geocoding

UP206A: Introduction to GIS

In a nutshell…

What is Geocoding?

» Geocoding is the process of assigning a location, usually in the form of coordinate values (points), to an address by comparing the descriptive location elements in the address to those present in the reference material.

Why Geocode?

» Many reasons. ˃ One is to be able to determine which boundary (e.g. school district,

census block, voting district) a particular address is contained.˃ To visually see if data is clustered or dispersed˃ To summarize data by a larger geography˃ Display points based on certain parameters

» To extract information from an address that the address does not immediately offer.

Geocoding Work Flow

The Data – What is Needed?

The Geocoding Process

Data Problems

» Inconsistent» Incomplete» Not in the correct

address format» Data not collected

for research purposes

Incorrect Address Formats

CODE ADDRESS

1 LOMA GRANDE ESTATES LOT 48

2 CAMINO DE LOS CHAVEZ

3 CASTLE APRT

4 2 MILES WEST OF CAPITAN

5 MM 278 HWY 70

6 PO Box 862

7 UNKNOWN

8 GENERAL DELIVERY

9 T16SR13E30

10 TRACT 2 MAP 70

Accuracy of Matches

» Are the points being placed where they should be?

» Depends upon accuracy of address and road network.

» Score» Informal Checks

˃ Compare against existing data, known points. ˃ Check against Zip Code boundaries, quadrants˃ Last resort: Check against Google, Yahoo online geocoders!