Extract the data at the source level and merge/join these data with the equivalency file, keying on the source geocode(s).30 years ago they were mostly created using base maps and clear plastic overlays. Geocorr is a likely source for such a correlation, but there are many other possible sources. The data must be available at the source geography level, and you must be able to correlate the source geographic entities to the target areas. Identify your source and target geographies, and the data to be allocated.But obviously there are many other programming options. We shall cite some SAS code because that is the language/resource we use for doing such processing. We assume that anyone wanting/needing to apply these methods will have some programming skills that will allow implementing the algorithm. We are not aware of any end-user-friendly applications that handle this allocation process. We'll include discussions of how reliable the results may be and look at a way of measuring the reliability of an allocation. Our examples will make use of equivalency files (aka "correlation lists" or "crosswalk files") generated using Geocorr. In this tutorial we want to focus on a few specific examples of doing source-to-target data allocations, outlining the basic algorithm and even pointing to some specific tools (in the form of SAS macros) that we have been using at the Missouri Census Data Center for more than 30 years. What we would like to be able to do is to process the data at the source geocode level to at least approximate data for the target units. This terminology will be familiar to Geocorr users, where you get to choose two kinds of geographic layers from select lists labeled as Source and Target geographies. We shall refer to the units for which we have data as the source geography, and the units for which we would like to get data as the target geography. For example, we might have 2010 census data for units such as census tracts and block groups within a state, but not for the state legislative districts (house and senate) of that state. data that summarizes a set of geographic entities) is that we have data for some geographic areas describing a universe (such as a county or state) but not for some other sub-units of that same universe which are of interest. Data Allocation Using Geographic Equivalency Files The ProblemĪ common problem encountered with using geography-based data (i.e.
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