The raw material for creating MCD Groups are lists of MCDs and precincts
(by precinct). These come from the 94 dataset which has numeric
census codes for both units. Because sometimes MCDs and precincts in
different counties have the same numbers, they are concatenated to the
three-letter county code before being input to plvdkey.exe . The input
is a text with one precinct per row, in the following format:
As an example, here are the first five lines of ia.mcd, the mcd and precinct plvdkey.exe input file for Iowa:
001085 0010101
001040 0010102
001095 0010103
001015 0010104
001020 0010105
In this example, the ``001'' at the start of each column represents county number one, and the remaining three and four digits are MCD and precinct codes, respectively. Because the parsing routines in plvdkey.exe input each column as text strings, they must be rectangular--hence the leading zeros to fill the column. The columns may be delimited by spaces or tabs.
An additional input file may be necessary if it is desired that some counties never be split into multiple MCD Groups. By default, multiple MCD Groups are created in all counties where possible. If an exception list file is provided, with the name filename.mge (in the same directory as filename.mcd), plvdkey.exe keeps the excepted counties as single MCD Groups. This might be required when hand-matching of precincts to corresponding precinct-level electoral data units in a county is discovered to be impossible by a hand-matcher. The solution to this kind of problem in practice is to enter all of the unmatchable counties into an exception (.mge) file and create new MCD Groups.
The format of the .mge file is to place the census county number one to a line, ended with a semi-colon. Comments may be added to the remainder of the line. For example, we find the following exception in Oklahoma's ok.mge file:
71; Kay County
This file is automatically read, if present, when plvdkey.exe is run on the input file ok.mcd.
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