Using TIGER/Line geographic data is a fundamental skill in geographic information systems (GIS) and data analysis. These files provide the spatial context for data, allowing you to create maps, perform spatial analysis, and visualize trends. Since the files themselves do not contain demographic data, the core process involves joining TIGER/Line geometry with separate census data tables.

 

How to use TIGER/Line geography, from obtaining the data to performing analysis.

 

Step 1: Obtain the TIGER/Line Data

The U.S. Census Bureau is the primary source for TIGER/Line files. The most common and user-friendly format is the Shapefile.

•TIGER/Line Shapefiles: These are the most comprehensive datasets and are a standard format for use in GIS software. They are organized by geographic feature (e.g., roads, census tracts, school districts) and by state or county.

 

You can download these files from the Census Bureau's website. The download process typically involves:

1.Selecting the year (or "vintage") of the data you need. It's crucial to match the TIGER/Line vintage to the year of the demographic data you plan to use.
2.Choosing the geographic layer (e.g., census tracts, counties, roads, water features).
3.Selecting the state and, for some layers, the county.
4.Downloading the compressed .zip file.

 

Step 2: Acquire Census Demographic Data

Since TIGER/Line files only provide the geographic boundaries, you need to get the actual data separately. The Census Bureau's primary tool for this is data.census.gov. Here, you can find a vast amount of data from the Decennial Census, the American Community Survey (ACS), and other programs.

 

When you download data from data.census.gov, you will get a table, typically in a .csv or .xlsx format. The key to linking this data to your TIGER/Line files is the Geographic Identifier (GEOID). This unique code identifies each geographic entity (e.g., a specific census tract or block).

 

Step 3: Use GIS Software to Merge the Data

This is the central part of the process. You'll need a GIS software program to combine the geographic files with the tabular data. The general workflow is as follows:

1.Load the TIGER/Line Shapefile: In your GIS software, open the downloaded .shp file. This will display the geographic boundaries or features on a map.
2.Load the sociometric data: Open the .csv or other data table you downloaded.
3.Perform a Table Join: This is the most critical step. You will join the demographic data table to the TIGER/Line shapefile's attribute table. You do this by matching the common field, which is the GEOID.
oThe TIGER/Line file's attribute table will have a field like GEOID or STATEFP + COUNTYFP + TRACTCE.
oThe demographic data table will have a corresponding GEOID field.
oOnce merged, each geographic feature on your map will now have all the associated demographic data attached to it.

 

Step 4: Map and Analyze the Data

With the data merged, you can now use the power of GIS to create compelling visualizations and perform analysis.

•Create Thematic Maps: You can create thematic maps (maps that use different colors or shades to show a variable) to visualize population density, median household income, or other demographic data by census tract or county.
•Perform Spatial Queries: Ask questions like, "Which census tracts have a poverty rate above the national average?" or "Where are all the roads within a specific school district?"
•Geocode Addresses: Using the road and address range data in TIGER/Line, you can take a list of addresses and plot them as points on a map. This is useful for market analysis, service planning, and more.

 

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