1. GeoCoder

1.1 GeoCoding Basics

1.1.1 What is GeoCoding?

GeoCoding is the process that assigns a latitude-longitude coordinate to a valid ZIP+4. Once a latitude-longitude coordinate is assigned, the data can be used for distance mapping or in a spatial search.

Melissa Data’s GeoCoder Object will attempt to return the coordinates of an address based on the ZIP+4^® code for that address. This (Plus4) centroid is usually compact and averages 9 households. In addition to Latitude and Longitude, the object returns Census Data such as Census Blocks, Tracts, County Names and FIPS numbers.

The Latitude returned by GeoCoder will always be a positive latitude as all US ZIP Codes^TM are situated north of the equator. The Longitude will always be a negative longitude as all US ZIP Codes are all situated west of the Greenwich meridian.

There are also methods like Compute Distance and Bearing which can be used to Calculate the distance between two Plus4s and their general direction.


1.1.2 What information does GeoCoder provide?

GeoCoder will provide the following information for a valid ZIP and Plus4 combination:
- Latitude
- Longitude
- County FIPS
- County Name
- Census Block Group

GeoCoder can also compute the distance and bearing between two latitude/longitude sets.


1.1.3 What type of Geodetic system does GeoCoder use?

WGS-84 is the geodetic system used in the object’s data to determine bearing and distance. WGS-84 is an earth fixed global reference frame, including an earth model.
This standard is used by the European Air Traffic Control and is a standard mapping reference used by many countries. All updates to GeoCoder are released on a semiannual schedule, and these include data from the 2000 census and the proposed Census changes for each calendar year.

1.1.4 How often is GeoCoder updated?

GeoCoder is released as quarterly updates (Spring, Summer, Winter, Fall) and is valid for 9 months after its release.

1.1.5 How accurate is GeoCoder?

The latitude and longitude data that GeoCoder uses is based on the Plus4. So, GeoCoder is accurate to the Zip+4.

1.2 Using GeoCoder

1.2.1 What are the differences between the COM and standard version of GeoCoder?

There are essentially no differences in the underlying code for the COM version and the Standard version of GeoCoder Object. The COM version has a COM interface layer used to communicate between your code and GeoCoder Object and is supported by many different languages. The Standard version of GeoCoder Object, and it is an unmanaged dll that must be included into your program which eliminates the extra latency created by the COM layer.

1.2.2 What should I do when installing GeoCoder?

When installing GeoCoder, always read the changes.txt file on the root of the CD. It will contain any changes that were made since the last release of GeoCoder. Some changes may require rewriting or recompiling your application, so it is important to always check the changes file.

1.2.3 What inputs are necessary for Geocoding?

The minimum input is a ZIP Code. If you enter a ZIP Code, GeoCoder will give you the latitude and longitude of that ZIP Code based on population density. (Closest to the most dense area of the ZIP Code) To get plus4 accuracy, you must enter both a ZIP Code and a plus4.

1.2.4 How do I use GeoCoder as a Distance Calculator?

GeoCoder can be used to determine the distance between two points. For this functionality, you only need the ZIP and Plus4 from the two points. That can be obtained using Address Object. Once you have that, run GeoCoder on those two locations and extract the latitude and longitude. Then, simply pass those two sets of latitude/longitudes into the ComputeDistance() method, and a distance of miles will be returned to you.

geoObj.GeoCoder(Location1ZIP, Location1Plus4)
Lat1 = geoObj.latitude
Long1 = geoObj.longitude
geoObj. GeoCoder(Location2ZIP, Location2Plus4)
Lat2 = geoObj.latitude
Long2 = geoObj.longitude
Miles = geoObj.ComputeDistance(Lat1,Long1,Lat2,Long2)

This can be used for applications like a Dealer Locator where you have a point of origin and several dealer locations. You would compute the distance from the origin to each dealer location and pick the one with the smallest distance.

1.2.5 How do I determine the bearing of a location?

GeoCoder can also compute the bearing of a location from an origin location. Bearing is the clockwise angle of the destination in reference to the origin with 0° being North, 90° East, 180° South, 270° west. Similar to ComputeDistance, the ComputeBearing method takes in two sets of latitude/longitudes. The bearing is returned as a degree ranging from 0 to 360.

geoObj.GeoCoder(Location1ZIP, Location1Plus4)
Lat1 = geoObj.latitude
Long1 = geoObj.longitude
geoObj. GeoCoder(Location2ZIP, Location2Plus4)
Lat2 = geoObj.latitude
Long2 = geoObj.longitude
Direction = geoObj.ComputeBearing(Lat1,Long1,Lat2,Long2)