1. Introduction

 

The US Census Bureau collects Census Data every ten years.  The census tract is part of a 4-level hierarchy of census data in which each lower level is completely contained within its parent level. The 4 levels are block, block group, tract, and county.  1940 is the first year that the Census Bureau started creating census tract maps.  Prior to the 1990 census coverage was not complete, i.e. for rural areas in 1980 there simply was no census data.  The main reason for this was due to the fact that there were not enough people living in these areas. Among the criteria that the Census Bureau has established for defining tracts is that they should be compact contiguous areas with populations of about 4000 persons and that the area should, if possible, try to avoid combining non-homogeneous areas.

 

Where tracts have existed for several decade there is frequently a correspondence between the codes used between one census year and the previous decade. Census tracts are assigned 4-digit numeric codes, unique within counties. Tracts can also have a 2-digit suffix code, usually indicating that this is a "split" of a tract from an earlier census year.

 

 

  1. Objective

 

                                I.      Create Census tract shapefiles from 1940-1970 for Austin TX.

The initial intent of this project was to create census tracts for 1940 – 1970, although I soon realized that I was also going to have to recreate the 1980 and 1990 as well.

 

                             II.      Populate attribute tables of newly created Census tracts                                        shapefiles with stf1 data that pertain to total population,                                                sex, and race.

 

                           III.      Evaluate Tract Evolution between 1940-2000

 

                          IV.      Analyze the growth within the population between 1940-2000 using two approaches:

 

  1. Data Sources

 

2000 Summary Tape File 1 (STF 1) data was downloaded from:

ESRI

http://www.esri.com

1990 Summary Tape File 1 (STF 1) data was downloaded from:

U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet

1980-2000 Census Tract shapefiles and Travis County road layer was downloaded from:

 UT Austin Community and Regional Planning

ftp://issweb.ci.austin.tx.us/pub/GIS-Data/Regional/census

1940-1970 census data was collected from the Dallas public Library

 

  1. Software Used

Ř      ArcInfo 9.0

Ř      ArcView 9.0

Ř      ArcCatalog 9.0

Ř      Arc Toolbox

Ř      Microsoft Office

 

  1. Historical back ground of Austin, TX. (Travis County)

When was Austin founded?                                                                                                                     “Waterloo was the name of the very small community that existed near the Colorado River and today's Shoal Creek before Austin was founded.  The site of Waterloo was purchased for the capital of the Republic of Texas in March 1839 and renamed in honor of Stephen F. Austin. On August 1, 1839, the first city lots were sold at auction. The city was officially incorporated on December 27, 1839.”

“By 1840 the city's population grew to 856, but in 1842 the President of Texas, Sam Houston, moved the seat of government to Houston and then to Washington-on-the-Brazos, which was the capital of Texas until 1845. During this time Austin's population had dropped below 200. In 1845 Texas was annexed into the United States and on February 19, 1846, Austin formally became the state's capital”

What is the oldest house in Austin?                                                                                                                                                               
”The French Legation, at 802 San Marcos, is Austin's oldest documented structure still on its original site. Construction began in December 1840 to the specifications ordered by France's representative to the Republic of Texas, Jean Pierre Isadora Alphonse Dubois de Saligny. The French Legation is now open to the public as a museum.”

 

 

  1. Methodology

 

                               I.      Collect data needed for the project

 

The majority of the data used for this project was not available online.  I had  to go to the Dallas Public library and scan the census tract maps and population data.  I was able to obtain 1980- 2000 shapefiles, and current roads for Travis County from the city of Austin’s web sight.

 

 

 

 

 

                            II.      Creating Census Tracts from 1940-1970

 

§         Scanning

 

The Census tract maps from 1940 to 1970 that I photo copied from the Dallas Public Library all had to be scanned into my computer in order for me to work with the maps.

 

§         Projecting / Georeferencing

 

The scanned images had to be georeferenced.  “Georeferencing is the process of establishing a relationship between the raster’s (row, column) coordinate system”.   In order to establish georeferencing you must use the georeferencing tool bar.   

This is a standard extension that comes with ArcView and ArcInfo.   

 

Once the general location where the scanned image needed to be located was established, I fit the image to the display.  Next I added control points to link the image to the exact location in space that it needs to be.   I chose to use the 2000 census tract shapefile as my guide. 

 

 

 

§         Topology/  Editing

 

After a few trial and errors, I found that it was easier to work backwards.  I copied the 2000 shapefile six times within a personal geodatabase,  and renamed the files as 1940 – 1990.  Then I started editing the data to match the associated year.  I found out several things while working through this process.  One thing is that there would have been no way that I could have created tracts that overlay exactly without the use of snapping.  Another thing that I found out is that when you are in edit mode and are trying to Auto-Complete Polygon, if the whole area that you are working on is not within the view area the shape will not be created.  I found that the use of transparency while editing the Census tracts was very beneficial.  It made it easer to see what I had deleted, and what I was going to delete.

 

 

 

 

 

 

 

                         III.      Populating attribute tables

 

I populate the attribute tables of newly created Census tract shapefiles with Summary Tape File 1 (stf1) data that pertained to total population, sex, and race. The source of the data that I used to populate the attribute tables of the census tracts all were originally published by the Census bureau.  I had to go about locating data for different years in different locations.  The data needed to populate the 1940-1980 tables all came from the City of Dallas Public Library.  The data used within the 1990 tract was downloaded from the US Census Bureau web site.  The stf1 data that I used with the 2000 Census tract was downloaded from the ESRI website. 

 

 

 

 

 

 

 

 

                          IV.      Evaluate the evolution of Austin, TX. (Travis County) from 1940-2000

 

 

§         Tract Evolution between 1940 – 1950

The tracts that were created between 1940 and 1950 were only of the City of Austin, they did not include all of Travis County.

 

 

 

 

 

 

 

 

 

 

 

 

§         Austin TX Tract Evolution between 1950 – 1960

 

 

 

 

§         Austin TX Tract Evolution between 1960 – 1970

§         Austin TX Tract Evolution between 1970 – 1980

 

 

§         Austin TX Tract Evolution between 1980 – 1990

 

 

 

§         Austin TX Evolution between 1990 – 2000

 

 

                             V.      Spatial Analysis of 1904-2000 Tracts

                     

I analyzed the Census tract data with two different methods to see how the results compared using the two approaches.

  

v     The first method I used was the “Union” approach.  This method allocates population based on land area.  This approach assume that the population is evenly distributed within the geographic area.  Unfortunately,  for the most part, this is not usually the case within the population. 

 

v      The second approach that I tried was the spatial join using Centroids.  The general idea is to convert the newer tract that is being analyses into points and then run your analysis.  This method is very useful when there are a lot of polygon spatial join overlaps.  This approach assumes that the geographic units “nest” into the older tract.  The 1990 and 2000 census tracts seem to “nest” within each other. However the older tracts have certain areas that do not have any correspondence within borders between the two sets of geographic units being analyzed.

 

 

 

 

v     I chose to only use the Union approach with the 1940-1960 Census tracts due to the fact that the boundaries between the boarders did not match up.  

 

 

v     Due to the fact that the bases of my analyses was to tract population change within Austin I only focused on this area when I created the layouts.

 

 

 

 

 

 

 

  1. Problems

 

                                I.      Georeferencing the scanned census tract maps from the 1940-1970.

 The problem was in large part due to the fact that the 1980-2000 Census shapefiles that I was working with are not that spatially accurate, there for it was hard to judge where exactly the scanned images should be repositioned.

  In order to overcome this problem, I decided to use the City of Austin 2000 Census tract shapefile to georeference the scanned images.  This seemed to solve the problem.

 

 

                             II.      The 2000- 1980 shapefiles that I downloaded from City of Austin website did not overlay properly.

 At first I tried to edit the data with topology, but quickly decided that it would be easier to recreate the tracts using the Census 2000 layer.

 

 

 

 

 

  1. Conclusion

 

In 1940 the total population in Austin TX was 87930; in 2000 the total population was 656,562.  The city has increased 646 % over the span of 60 years.

 The use of the two differed methods generated slightly different results.  I am not sure if one way is that much more accurate than the other.  The population change in Austin had been sporadic over time, with no apparent trend in population change.

 

 

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