The basis for an advocacy system is being able to determine which legislative districts your advocates reside in and/or work in. This is typically done by using your advocates home or work address and comparing it to the geographic coverage that is used to define legislative district lines. The US census bureau keeps track of neighborhood geography, monitoring growth and changing the definition of geographic areas to reflect changes in population distribution. In simpler terms, when the land is developed and new streets are put in or new houses are built the census bureau tries to capture that information so it can be used to collect data in the decennial census. That new shopping center in your neighborhood has probably lead to new houses being built on land that was not developed 10 years ago. This means that while there were no people on that land ten years ago when they did the last census, now it is populated.
Every 10 years the US Census Bureau conducts the decennial census to collect population counts. They have their own set of geography that they use for the census, starting with the state area, then the counties. Within the counties they define census tracts, and within census tracts they have block groups which are composed of census blocks; the land area covered by four street intersections that make up a block. Once the census bureau gets the initial counts of population by race from the decennial census, they distribute those files to the states that then use the data to redefine the legislative districts to reflect the new population and balance the racial distribution of the population within districts. This process, known as redistricting, uses the census blocks (of which any given state can have hundreds of thousands of blocks, even up to a million) to create districts by grouping the census blocks. At the end of the process, each state has a list of all the census blocks within each State House, State Senate, and US Congress district in that state.
Your advocacy system is affected by the redistricting process because it often changes the assignment of a census blocks and that block’s population count. If a district boundary went through farmland that was uninhabited ten years ago and now that same area is a housing development, you may have one census block for the farmland in the 2000 census and 10 new blocks from the current census with population in each. Of those 10 new blocks, 5 may be in the same district as the original farmland but 5 may now be in a different district because the population count changed the boundary line for a house or senate district.
If you have an advocacy system where advocates are linked to their legislative districts, you need to change the base year to 2010 and use the redistricting files from each state. Advocacy systems that use ZIP codes to assign legislative districts are not as accurate as those that use census blocks because postal geography does not conform to census geography. A zip code boundary may go down the middle of a census block and even ZIP + 4 geography may also split the border of a census block, so your resulting assignment to a district may be inaccurate.
The best district assignment process is to have your advocate file geo-coded to their census block. This process takes the street address and matches it to a census street address database that shows every street address range (1-50 main street) and what census block it corresponds to. This process uses the same geography that is used to define legislative districts, so there is no ambiguity in the district assignment.
The new legislative districts have already gone into effect in Louisiana and must be in place for the upcoming elections in November in all states. If your advocacy system is not based on 2010 geography by November, then you will be out of sync with the areas covered by your elected officials. Not a good way to start 2013.