Peter S. Wattson
State of Minnesota
Minnesota Census Data Center
1990 Annual Conference
St. Paul, Minnesota
November 28, 1990
The purpose of this paper is to explain how the Minnesota Legislature plans to use the Census Bureau's TIGER files to change the boundaries of Minnesota's legislative and congressional districts following the 1990 census. My aim in doing this is twofold: first, speaking to you as technicians, to make you aware of yet another use to which a geographical information system can be put; and second, speaking to you as citizens of a democracy, to make you aware of the political process that will be occurring over the next two years to redraw the political map of the state.
II. Redrawing the Political Map
Redrawing a political map seems like it should be a simple matter. You
take a good map of the state, decide where you want the new district boundaries
to run, and draw the new boundaries on the map.
The standard for congressional plans is that the districts must be "`as nearly equal in population as practicable.'' Wesberry v. Sanders, 376 U.S. 1 (1964). This has come to mean that, where there are competing plans, the plan with the lowest overall range, that is, the difference between the largest and the smallest district, wins. Congressional districts across the United States vary in size, but normally are about half a million people. The overall range of congressional districts in Minnesota after the 1980 census was 46 people. The overall range of congressional districts in Colorado was 10 people. You can't get that kind of precision by drawing on a highway map. Why not? Because the Census Bureau doesn't use highway maps for conducting the census and reporting population. The Census Bureau draws its own maps, using the TIGER files.
One of the main reasons the Census Bureau decided to create TIGER for the 1990 census was to eliminate discrepancies between census geography, as shown on census maps, and census population counts, as shown on tapes and printed reports. In 1980 and before, there were blocks on census maps for which there were no population counts, and population counts in census tables for which there were no blocks on a census map.
A second reason for creating TIGER was to reduce errors in assigning population to the correct unit of geography. In 1980, census counts were often assigned to the wrong block, city, town, or county. Most of these errors were detected in the process of post-census local review, but others only came to light as legislative staff were trying to make the new districts fit within an acceptable overall range. Needless to say, when we in Minnesota were struggling to reach an overall range of 46 people, these discrepancies and errors were cause for some concern.
Now, the basic unit of census geography is the block; but the basic unit for election returns is the precinct. One of the major additions the Census Bureau has made to its mapping data base as part of creating TIGER is the addition of precinct boundaries. Phase 1 of the Census Bureau's 1990 Census Redistricting Data Program was a cooperative effort with the states to correct and add block boundaries that the states anticipated might be useful for redistricting, and Minnesota was one of the leaders in that effort. Phase 2 was the addition of precinct boundaries. Minnesota was one of the first two states in the nation to finish providing its precinct boundaries to the Census Bureau last fall, and expects to get them back in electronic form as part of the Initial Voting District Codes TIGER file this fall. The addition of the precinct boundaries to the TIGER file will enable legislators to relate data from election returns to census geography and know, not only how many people are in a precinct, but how they have voted in the past.
In Minnesota, the difficulty is even greater, since two house districts must be nested within each senate district. A plan for house districts must be drawn so that it also secures the support of a majority of the senate members, and a plan of senate districts must be drawn so that it also secures the support of a majority of house members.
Now, its true that the legislature acts by passing a law describing the metes and bounds of the new districts, rather than by enacting a map. But for purposes of explaining a plan to the members who are asked to vote for it and to the state, county, city, and town officials who must conduct elections in accordance with the plan, a good set of maps is essential.
I have been told that, after the 1980 census, Minnesota was the only state in the nation that had a digitized computer map of the entire state that it used for redistricting. When the Senate had agreed on a redistricting plan, we tried plotting it on our computer. We were horrified by the results. We used a pen plotter, which was horribly slow, so we could not possibly take the time to plot more than the borders of the new districts. Borders without the names of the physical features they ran along or the census units they enclosed were worthless in explaining to members what was in their new districts. Back to the highway maps. We tried laying the border maps over highway maps to trace the new boundaries on the highway maps, and found they didn't match. Wrong scale. Wrong projection. Different control points. Different coordinates. County edges did not match. Blocks of water ran along rivers for miles. Block polygons did not close. Not to mention different city boundaries in areas where there had been annexations. It was a major effort to translate the legislative district boundaries created by aggregating census units in our computer system into boundaries we could trace by hand on base maps the members had some faith in.
I never did see a high quality map of the 1982 legislative and congressional districts until long after the Legislature had given up on trying to agree to a set of plans, the three-judge federal court had adopted a set of their own, and the elections were underway. That was a map the Secretary of State obtained from Larry Charboneau's company, Lawrence Mapping and Graphics.
The TIGER files we receive from the Census Bureau will allow us to tie population counts and election returns to census geography, but they will not allow us to assign census units to districts or to plot maps or print reports analyzing those districts without the assistance of software we must purchase from a vendor. And they will not allow us to plot maps of a quality sufficient for presentation to legislators and election officials without substantial additional work to improve the TIGER files.
III. Improving the TIGER Files
A geographic information system is an expensive proposition. It takes a lot of time and money to assemble. You don't want to throw it away after only one use. You want to maintain it.
But geography changes over time, so you need to be conscious of what time the data in your GIS represents.
Several months ago, when I first talked to Linda Tomaselli, my heart went pitter-pat at the news that she and the Metropolitan Council were planning to improve the TIGER files by updating the streets in the metropolitan area to January 1, 1989, by starting with the Minnesota Department of Transportation's digital street file and rubbersheeting the pre-census TIGER file's streets to it, since that meant that the cartographic quality of the TIGER files might at last be brought up to presentation quality within the GBF/DIME file area, and that we could show on our maps the streets that had been graded up to that date. I hope you all can now appreciate what a major improvement to the cartographic quality of the TIGER file this will be. The Subcommittee on Redistricting has contracted with the Metropolitan Council to provide this improved TIGER file to us for use in redistricting.
Outside the seven-county metropolitan area, the Minnesota Department of Transportation has been digitizing its county map series. The counties adjoining the metropolitan area have been completed and are being kept current. However, the county maps contain only state and county highways, they do not contain city streets, so city streets outside the seven metropolitan counties have not been digitized and will not be digitized in the near future. MnDOT has been maintaining city streets outside the seven-county metro area only on paper maps, which are updated following each construction season. Any update of the TIGER/Line file of city streets outside the metro area, beyond what is done by local officials as part of the Census Bureau's local review program, will have to be done using the MnDOT paper street maps. This should not be too big a job, since there have not been many new streets added since 1986 outside the metropolitan area and its adjacent counties.
The Subcommittee on Redistricting has recently contracted with the State Planning Agency's Land Management Information Center to examine the TIGER files for a sample of the 80 nonmetropolitan counties and report by the end of this month on the time and cost required to update and improve the cartographic quality of those TIGER files for use in redistricting.
The boundaries used by the Legislature for redistricting must coincide with those used by the Census Bureau in order for the population counts to be accurate. So the districts drawn on those old boundaries may unintentionally split newly-annexed areas away from the city to which they were annexed. Avoiding that will be another headache for legislative staff who must work with cities like Stillwater, Farmington, New Prague, and Rochester.
To correct the file to show the precinct boundaries actually used for the 1990 election, it will be necessary for the Subcommittee on Redistricting to consult the files of the Secretary of State to determine which boundaries have changed since 1988, and compare the Phase 2 maps, the maps produced using the IVDC file, and the most recent maps on file with the Secretary of State and the State Demographer showing the boundaries used in the 1990 election. The precinct boundaries in the IVDC file will then have to be manually adjusted forward to create the 1990 boundaries and backward to create the 1988 boundaries. A similar technique will be necessary to create the 1986 precinct boundaries.
The 1984 precinct boundaries will be more difficult to establish, since the State Demographer has not kept precinct maps from before 1986. The Subcommittee will consult with the State Demographer about how best to locate these old maps from the city clerks affected.
Outside the metropolitan area, we assume that address ranges in GBF/DIME file areas date from 1980, and that elsewhere they are simply blank. The Land Management Information Center's examination of the nonmetropolitan counties should tell us more about that. We are still looking for a way to add address ranges to those TIGER files at a reasonable cost.
IV. The Census Version of TIGER
Before April 1, 1991, at about the time it delivers to each state the block-level population counts needed for redistricting, the Census Bureau will deliver the census version of TIGER, incorporating the final geography used to tabulate the 1990 census and including all corrections received from local units of government and processed by the Bureau.
One problem the Subcommittee is now wrestling with is how to provide the improvements we make to the TIGER files to the Census Bureau in a form they can use.
The Census Bureau is now equipped to accept changes only if they are drawn by hand on Census Bureau maps. We simply do not have the resources to undertake drawing all our planned changes on paper maps, and neither do most other users of the TIGER files we have talked to. But it is in all our interests to keep the TIGER files up to date, so we are now exploring with the Census Bureau whether it may be possible to develop a method for submitting these changes electronically. I have some hope we will succeed.
V. Adding Population and Election Data
Whether the legislature adopts legislative and congressional redistricting plans or fails to do so, I assume there will be a lawsuit asking a three-judge federal court to do it better. When that happens, I expect to be in court once again, using maps and reports produced with the aid of the TIGER files to advocate the Senate's position.
Minnesota Statutes, section 204B.14, subdivision 3, requires local governments to establish new precincts within 45 days after the legislature has been redistricted, but no later than May 10, 1992, so that no precinct lies in more than one legislative district. Cities with wards must redraw their ward boundaries by the same deadline in order to meet one person, one vote requirements. Other election districts must be redrawn within 65 days after the legislature has been redistricted, but no later than June 1, 1992.
So the local governments don't have much time to redistrict themselves once the legislative districts are done, and some have inquired about getting redistricting data from the Legislature in electronic form. The Subcommittee on Redistricting has asked the Land Management Information Center to act as a service bureau for distributing electronic redistricting data, at the cost of providing copies, to anyone who requests it. The specifics of when and how that would be done have not yet been developed.
There are at least two kinds of data that could be provided. One would be a simple flat ASCII file of the redistricting plans, in PL 94-171 format, showing the legislative and congressional districts to which each census block has been assigned. That file should be relatively small and readable by any computer system, regardless of the software being used. The second would be the geographic and population data files. They would be much larger and would present more of a problem for various kinds of software to import. But if we can develop a way to convert our ARC/INFO files back into TIGER files for purposes of providing updates to the Census Bureau, we may be able to make the same conversion for purposes of providing our improved TIGER files to local units of government. The software to do that has not yet been written, but the Subcommittee has asked LMIC to explore the possibility of writing it.
I understand that the Secretary of State's office will be conducting meetings with local election officials in the course of the next year or so to discuss these issues further with them.
I hope I have told you what you wanted to know about using TIGER files for redistricting in Minnesota. If you have any questions, I would be happy to try to answer them.
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