Basics of Geocoding (use the mouse or down arrow to proceed at your own pace)

1. Basics of Geocoding(use the mouse or down arrow to proceed at your own pace) • Geocoding = putting an address on a map, a.k.a assigning latitude and longitude (x and y coordinates) • Geocoding against a street centerline (like Thomas Brothers map or Google Maps) follows a general algorithm • Find a zip code and a street (or a city and a street) • On that street, find the correct block based on the number range • On that block, find the correct side of the street – odd or even – and interpolate the address • 150 Main Street will be placed in the middle of 100 -198 block of Main St on the right-hand side • 175 Main Street will be placed 3/4 towards the end of 100 -199 block of Main St on the left-hand side • Buildings usually are not located at the edge of the street, so it is important to specify an offset • If no offset (e.g. 25 feet) is given, the geocoded point will be placed in the middle of the street line • Street number ranges do not necessarily represent the true number of buildings on the block • Geocoding against parcels (tax assessor’s boundaries of property) places the point either in the geometric center of the parcel or geometric center of the building footprint • Geocoding can be done with an exact address, street intersection, zip code, city, county • If geocoding against counties, zip codes, etc (polygons), geocoded point will be placed in the geometric center of the polygon • For census tracts and zip codes, it is possible to put the point in the population-weighted center (i.e. the center of where the majority of population is aggregated) • Note: Zip codes are postal delivery routes and do not have physical boundaries; zip code maps are approximations at best Created by Svetlana Smorodinsky, CDPH, DEODC-EHIB; updated Fall 2009

2. 50 Buildings 25 Buildings 150 100 198 200 250 300 Main Street 101 199 201 259 301 Medium Ave Small Avenue Large Avenue 96 80 80 84 98 100 90 Broadway 89 91 81 99 101 93 A. 150 Main Street, My City, CA 90001 A. Street centerline geocoding, with and without offset, geocoded point placed correctly B. Street centerline geocoding, with offset, geocoded point placed incorrectly (interpolation inaccuracy) C. Street centerline geocoding, with offset, geocoded point placed incorrectly (offset inaccuracy) D. Parcel geocoding, geocoded point placed correctly in the parcel centroid B. 80 Broadway, My City, CA 90001 C. 93 Broadway, My City, CA 90001 D. 96 Broadway, My City, CA 90001 With offset Without offset Parcel Geocode Created by Svetlana Smorodinsky, CDPH, DEODC-EHIB; updated Fall 2009