How to Create a Census Map

GIS in Planning and Health

Go to http://www.census.gov site to download the census data that you would like map.

•Select “American Factfinder” (this will provide the census data)•Go to “DataSet” section

Choose “Decennial Census”

•In 1990, there are STF1 & STF3.•In 2000, there are SF1 & SF3

STF: Summary Tape FileSF: Summary File

SF1: 100 percent household survey population & householdSF3: sample survey (1 out of 6 households)

Since we are interested in mapping “Median Household Income” at the census tract level we will choose 2000 Census SF3.

The site provides 1990 and 2000 Census data.

We need define following:

- Area of Study Area (define the area)- Spatial Unit (I.e., county, municipality, census tract, etc.)- choose variables that we are interested.

In this case, we choose all the census tracts for Middlesex County in New Jersey.

The next step is choosing a variable that you are interested.

•Choose the desired variable•Click “Add” •Click “View Result”

This is the result. We need to convert this data into Database file (DBF), so itCan be joined to census tract boundary file (Middlesex County).

To download the file, You click print/download menu, and click “download” menu.

Fortunately, US Census provide theData in the form that we want.

Click “Microsoft Excel” from Database compatible format

When you download, the website will provide output.zip file. You need to upzip (extract) the file, and put those files into your working directory (in our case, c:\GIS directory)

There are several different files. You need open the following file and convert it into database format which can be joined to Census tract boundary file.

Dt_dec_2000_sf3_u_data1.xls

This is the file when you open with Excel. The data needs to be organized into a database compatible format.

Here are several rules to follow:-make sure you identify which variable is going to be used as a key column (variable) for data joining-There only needs to be one title per row, the second can be deleted-Variables need to be renamed:

-Less than 9 characters-No special characters-Meaningful variable name (I.e., Median Household Income can be named “MHINC”)

- If there are any decimal points you need to keep and define by using format-cell function- Before you save as (DBF IV format), make sure you put your cursor in A1 cell.- In this exercise, we save the file as “MHINC.dbf”. - Make sure you save the file in your working directory (c:\GIS)

This is the sample excel file. For mapping purpose, we only need a key column (a unique identifier for census tract), and variables (the ones which we are interested in mapping).

Save the file as “MHINC.dbf”.

Now we need to download 2000 Census Tract boundary from http://www.geographynetwork.com

•Once you download the file, make sure that you have a “*.prj” file (projection definition). (The geographynetwork.com does not provide metadata)•The metadata can be founded at http://www.census.gov/geo/www/tlmetadata/metadata.html

So first thing you have to do is “to define projection” for the shape file you downloaded.

To define a projection for shape file, you need to click “ArcTool Box” (the red tool box) •Go to Data Management Tools•Projections and Transformation•Choose “Define Projection”

You need to enter the shape file you just downloaded and select the appropriate projection in order to define projection.

By looking at our metadata, we know that the data we downloaded from geographynetwork.com is

• Geographic Coordinate System (lat./lon.)• NAD83 (North American Datum 1983)

To be able to join the data from another table, we need to identify which variable can be used as a key variable. In this case, we can use:

“STFID” from tgr34023trt00 file and “CTRACTID” from MHINC.dbf file.

In this example, we will use STFID and CTRACTID to combine the two databases because they hold the same data and will correspond with one another.

To join data file, you right-click on the tgr34023trt00 and get menu, and choose Joins and Relates. Click Join.

You need to choose corresponding variables and table. After you click OK, you will have “Create Index” box, click Yes.

Once you click OK button, nothing happens on the screen. But the data is already joined. We can view by checking attribute table.

This is the outcome. We are almost there.

You can create a thematic map using the census data you have joined to your layer.

Make sure you use a right project for data frame.

There are two choices.

-You can add a shape file which has NJ State Plane coordinates(NAD83)-Or you can edit by right-clicking the Layer and manually change