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CensusCD 1980 in 2000 Boundaries

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CensusCD 1980 in 2000 Boundaries allows users to access US Census data from 1980 and easily compare it with the 2000 Census data. It is the first and only source of Census data from 1980 that is expressed at all of the 2000 Long Form geographies. The CensusCD 1980 in 2000 Boundaries contains both the 1980 Long Form (STF-3) and Short Form (STF-1) datasets. It includes detailed demographic data about topics such as population, household structure, income, poverty, education level, employment, housing costs, immigration, and other variables. The 1980 in 2000 Boundaries is an invaluable resource for policy makers, community organizations, and researchers who want to analyze the changes that have occurred in the U.S. from 1980 to 2000.

Additionally we have made the 1980 data more accessible than in the straight CensusCD 1980 – because we have normalized the data to the 2000 boundaries it means that the entire country can now be viewed at the Block Group, Tract and MCD level. In the official 1980 census only urban areas had tracts and block groups. We have also added MSA, CMSA, and PMSA geographies, whose concepts were being formed in the late 1970’s and early 1980’s but whose geographic boundaries were not yet assigned in the 1980 census.

Why Normalize 1980 Data to 2000 Geographic Boundaries?
Geographic boundaries change from census to census which means if you want to look at the changes in the data from 1980 – 1990 – 2000 then you need to deal not only with the demographic changes but also the geographic ones. By and large, county boundaries are stable over time but tracts and block groups regularly change from one census to the next.

In 1980 there is the additional issue of un-tracted areas that needs to be dealt with. The U.S. Census Bureau only tracted those areas that were considered "urban" or part of a metropolitan area. Below is a map of the entire U.S. with the 1980 tracted areas shown. (Map created by GeoLytics’ CensusCD 1980)

US Census Tracts in 1980

The definition of "metropolitan" has also changed in the past 20+ years. Areas that we now see as the suburbs of large cities were still farming communities in 1980. For example, when we look at the current definition of the Fort Wayne MSA (comprised of Adams, Allen, De Kalb, Huntington, Wells, and Whitley counties) one of the counties was not tracted (Whitley) and another (Huntington) was only partially tracted in 1980.

2000 Fort Wayne MSA with 1980 Tracts Boundaries

2000 Fort Wayne MSA with 2000 Tract Boundaries

This means that if we want to see how the current Fort Wayne, IN metropolitan area has changed, we are missing information for these tracts.

CensusCD 1980 in 2000 Boundaries fixes this problem – we have normalized the data to the 2000 tracts – thus the entire country is tracted. Because we have taken the MCD’s and counties and normalized those areas that weren’t already tracted to the tract and block group, it means that we can now look at the 1980 data at the tract level for the entire country.

Why is normalizing data such a big deal?

Changing track boundaries mean that it is difficult to compare track data over time. In the example below, a section of Allen County, IN is shown broken-out at the census tract level. At a glance, one can observe that there are changes in the census tracts from 1980 to 2000. In fact, Allen County, IN has a nice example of tracts merging, splitting, and merging/splitting into new parts. Overall, the number of tracts grew from 82 in 1980 to 90 tracts in 2000, a 10% increase.

Subset of Tracts in Allen County, IN in 1980 Boundaries

Subset of Tracts in Allen County, IN in 2000 Boundaries

Taking a closer look at Allen County from 1980 to 2000 reveals the modifications in tract boundaries that significantly impact how researchers study and account for changes in a population over time. For example, the single 1980 Tract # 011601 broke into two tracts in the 2000 Census (011601 and 011603). It is a straight-forward 1-to-2 correspondence. There are also mergers where two tracts, 002200 and 002400, merge into 1 tract 002200.

However, the changing tract boundaries from 1980 to 2000 are not always that straight forward. In the next example, tracts 011603 and 011701 merge and then split into three tracts, 011604, 011605 and 011701. The correspondence in this case is 2-to-3. It is made more complicated because if you don’t look carefully it appears that 011701 stays the same, it has the same code and the same general position. It may in fact even have the same centroid lat/long coordinate. But if you look carefully you see that there is a piece of the bottom of 011603 that is no longer part of 011605 but rather has been added to 011701.

There are other more complicated examples that have 2 or 3 tracts merging and splitting into 6 new tracts. From these examples in Allen County, it becomes evident why it is so difficult for researchers to contend with the issue of changing geographic boundaries over time.


        

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