Conversion and Assignment File Collection
Conversion and assignment files are used for translating data from one geographic unit of analysis to another.
Assignment files are used to assign one geographic unit to another when there is no overlap between the geographic units. Assignment files generally have two columns, one column indicating the geographic unit to be assigned and the second column containing its corresponding assignment to the other geographic unit.
An example of one of our most commonly used assignment files is our block to district assignment file. This file contains the census block numbers and their corresponding assignment to a given set of districts such as Assembly, Congressional, Senate, or the Board of Equalization districts. This is possible because census blocks do not cross district lines and as such they are either wholly within a given district or they are not.
Conversion files become necessary when there is overlap between geographies and as a result a geographic unit can not be wholly assigned to another as it is only partially contained within another geographic unit. In this case, its neccesary to 'translate' the geography from one geographic unit to another. Therefore conversion files will have a third column indicating the ratio of the geographic unit contained with in the other.
For instance, census tracts will often only be partially contained within a given census place. In this case, a census place to census tract conversion file can tell you what portion or ratio of a census tract is contained with a given census place. These ratios can be determined using either the census block population of the tract contained with the census place or the percentage of area of the tract contained with in the census place.
2010 - 2002 Precinct Conversion Files: Precinct boundaries change with every election. The precinct conversion files available on the Precinct Geography and Conversion pages are used for merging precinct data to other geographic areas such as census blocks and cities.