Basic Steps for Finding Demographic Data from the U.S. Census Bureau Website

VI. DAY 1: Afternoon

Census Data Exercise

Basic Steps for finding Demographic Data from the U.S. Census Bureau Website

Using American Factfinder: This portion of the Census website allows users to locate areas of interest in the U.S. with reference maps and discover what blocks, block groups, census tracts, or other census geographic units cover the area of interest. It also allows users to select desired census attributes and create a thematic map or export a table of the desired attributes for specified census geographic unit(s). To access Factfinder:

1. Go to the U.S. Census Bureau’s main web page at:

1. Select the link for American Factfinder or go to:

A. Identifying census geographic units with reference maps:

For example, if you want to find out what census tract covers Yale Campus in downtown New Haven, you would use the reference maps to find Yale, then get the census tract code that can be used in creating a thematic map or extracting a table of attributes.

1. Select the Data Sets link from the Factfinder web page.

1. Select the summary file and year you want (ex. Census 2000 Summary file 1, 1990 Summary Tape File 1, etc.). Note that there are different attributes available for different summary files. For example, summary file one typically has basic attributes like total population, sex, age, race, etc. where summary file 3 typically has cross-tab attributes like age by language spoken at home by ability to speak English for the population 5 years and over, and economic attributes like average housing value and median income. To see a list of attributes for the 2000 summary files 1 and 3, .pdf files at the following web sites can be accessed:

These are long documents with several hundred attributes to choose from. If you just want to look at attributes and codes, start with Chapter 7, Table Matrix. The rest of the document explains the geography and attribute definitions in more detail.

1. For this exercise, select ”Census 2000 Summary File 3 (SF 3) - Sample Data.”
   
2. After selecting a summary file and year, a menu will appear to the right of your selection. From this menu, select Reference Maps.

1. The reference maps page will bring up a map of the United States. You can identify your area of interest by either zooming in on the map or by using the menu on to the left of the screen that shows Reposition on… The reposition on menu gives you a choice of typing in an address or latitude or longitude.

1. In most cases easiest likely way to identify a place is by address. So for this example, type in an address or intersection, like “Huntington and Prospect, New Haven, CT.” The reference map will then zoom to the address that you entered. To the left of the map you will notice a legend that shows the symbology for the census geographic units like blocks, block groups, and tracts. Within the map, the codes for these geographic units will be labeled according to the color in the legend. For the address listed above, the census tract code is 1418.

B. Creating a thematic map

1. If you are still on the reference map, find the menu that has “You are here: Main> Data Sets> Geography> Results” and select the “Data Sets” link. This will take you back to the menu where you can select the link to Thematic Maps. Make sure you still have ”Census 2000 Summary File 3 (SF 3) - Sample Data” selected and click the Thematic Maps link.

1. Next, you will select your geography. For this example, we will select Place, so we can find Census tract 1418, which covers the address we found in the previous reference maps section. Subsequently choose the State (Connecticut), and Geographic Area (New HavenCity). Note: you can only select one geographic area for thematic maps. You can optionally click the Map it link to preview your area of interest to make sure you selected the right area. Then click the next button.

1. The next step is to select a theme. Note: You can only select one theme (attribute) for thematic maps since the map can only show one attribute. For this example, select TM-P063. Median Household Income in 1999: 2000 and click Show Results. A thematic map will be drawn for New HavenCity showing Median Householdincome, by census tract, symbolized into 5 data classes.
   
2. Use the “Display map by:” drop-down and change the display to “Block Group.”
   
3. Again, you can identify your area of interest by either zooming in on the map or by using the menu on to the left of the screen that shows Reposition on…, entering the “Huntington and Prospect, New Haven, CT” address again.

1. You can change the symbology and number of classes from the menu to the left of the map. If you have a pop-up blocker for your browser, hold down the control key on your keyboard when refreshing your map.

C. Creating and Exporting an Attribute Table

1. If you are still on the thematic map, find the menu that has “You are here: Main> Data Sets> Geography> Results” and select the “Data Sets” link. This will take you back to the web page where you can select the link to Detailed Tables.

1. On the Select Geography page, select block group as the geographic type for this example followed by State (Connecticut), county (New Haven), and tract (1418). For the block groups, select All Block Groups and click Add, then click Next. Note: you can select more than one block group for detailed tables. You can also select more than one census tract if you select a larger unit such as county for your geographic type.

1. In the Select Tables web page, select the desired attribute(s). For this example, chose P1 (Total Population), P6 (Race) and P53 (Median Household Income). You can select more than one attribute by holding down the control button on your keyboard. Click Add, then Show Result. This will bring up a table with the geographic units (block groups 1 - 4 for census tract 1418 in this example) in the columns and attributes in the rows.

1. To export or print the table, select Print/Download on the menu above the table. You can download the table as a .csv or Excel file (.xls), or .txt file.

D. General notes about Census Demographics

Census geography is basically divided up into 5 basic units of state, county, Tract, block group, and block, with the block being the smallest unit of geography. States and counties conform to normal State and county boundaries for the United States. Tracts, block groups, and blocks all fit within their larger units of geography without overlap. These boundaries are determined by population and not by a set value of area. Therefore, a block in New York city would be much smaller than a block in rural Montana (where there is a much smaller population density).

Census geographies do change every decennial census, so if you are doing a time-series study, keep in mind that some blocks, block groups, or tracts may not have the same boundary compared to an earlier or later census. Since the population changes every 10 years, the geographic boundaries do as well (since they are based on population).

A common mistake made by people using census data is including “Hispanic” as a racial group. According to the census, “Hispanic and non-Hispanic” are ethnicities and not races, so never mix “Hispanic” in with race categories when comparing census statistics.

For more information on using GIS for Census analysis, contact the GIS Specialist (Abraham Parrish) at the Yale Map Collection (, 203-432-8269,

Explanation of Census Geography

/ Through its many surveys, the Census Bureau reports data for a wide variety of geographic types, ranging from the entire United States down to a Census Block. The geographic typesthat a survey reports on will depend upon the survey’s purpose, and how the data were collected.

The diagram shows the many geographic types for which data are available in FactFinder. In general, larger geographic types (e.g., state) are shown near the top and smaller geographic types (e.g., census tract) are shown towards the bottom.
With connecting lines, the diagram also shows the hierarchical relationships between geographic types. For example, a line extends from states to counties because a state is comprised of many counties, and a single county can never cross a state boundary. To uniquely name a county, the state name must be included (e.g., Orange County, California; Orange County, Florida).
If no line joins 2 geographic types, then an absolute and predictable relationship does not exist between them. For example, many places are confined to one county. However, some places extend over more than one county, such as New York City. Therefore, an absolute hierarchical relationship does not exist between counties and places, and any tabulation involving both these geographic types may represent only a part of one county or one place.
Notice that many lines radiate from blocks, indicating that most geographic types can be described as a collection of blocks, the smallest geographic unit for which the Census Bureau reports data. However, only two of these lines also describe the path by which a block is uniquely named. That is, the path through the Block Group or through the Tribal Block Group.
Note: To read definitions of the geographic types, click Glossary on the banner of American FactFinder. /

Basic Steps for finding Demographic Data on the ESRI Website

Using ArcMap: ArcMap is part of ESRI’s ArcGIS package and allows you display & analyze geographic data. ArcGIS is only one type of Geographic Information System (GIS), there are other software packages that have similar capabilities. ArcGIS is available in the FES computer labs.

E. Retrieving spatial data for ArcGIS

1. The ESRI website has datasets that are free to download. The 2000 Census data is available at :
2. Select a State, submit selection. You then have the option to select data by data layer or by county; select by County.
3. You can then select particular attributes or choose to download all data layers. We have downloaded these files for you. They can be accessed from a shared server. We downloaded “ALL DATA LAYERS” from the Census 2000 Tiger/Line® website. This file contains several zipfiles, each containing a shapefile and/or a table of census data. You will also notice the “readme.html” file. These “readme” files are very important and often serve as a sort of decoder ring for the abbreviated file names; for example trt00 = 2000 census tracts and lkA = roads.

NOTE: Data can also be retrieved from the American Factfinder website (see above) and brought into ArcGIS, though it is a bit trickier.

Introduction to ArcGIS & Mapping

Preparation & Introduction to ArcMap

1. Using your Web Browser, Browse to the Yale Map Collection website at .
   
2. On the right side of the front page, Find the Quicklinks and Click on the “Download GIS Workshop Materials.”
   
3. Scroll to the bottom of the page to find the “Yale Mods 2007 – Urban Forestry Workshop” materials. There will be documents and a related dataset available.
   
4. Download the Urban_Forestry_Workshop.zip file to a folder on which you have write permissions (typically, you will be able to write to the C:\temp folder, but your work may be deleted when the machine reboots).
   
5. Browse to the folder where you downloaded the dataset (for the purpose of this guide, we will assume it is the C:\temp folder, as mentioned above) and Create a new folder using your initials. For example, if your name is John Jacob Jinglehymer-Smith, you would make a new folder called C:\Temp\JJJ.
   
6. Unzip the dataset to your new ‘initials’ folder. From this point, we will refer to this main folder as your ‘initials folder.’
   
7. Browse into your initials folder and find the C:\temp\your_initials\Urban_Forestry_Workshop\Data\Shapefiles folder.
   
8. Take a look at the files in this folder. Note that many of the files in the folder have the same names, but different file extension (.dbf, .prj, .shp, etc…). Each set of similarly named files makes up a single “shapefile.”
   
9. Return to the C:\temp\your_initials\Urban_Forestry_Workshop folder and look for the file called Urban_Forestry_Workshop.mxd and double-click it to open it with ArcMap.
   

The ArcMap Interface

Once you have opened the Urban_Forestry_Workshop.mxd file, you should have something like the above image. Highlighted are the following important elements of the ArcMap interface:

• Table of Contents – This panel shows the data ‘layers’ that re included in your Map Document. Each layer’s visibility & Symbology are displayed here. Right-clicking on any layer’s name provides access to a context menu with several options for interacting and altering the Map Document, relative to the data layer.
• Map Document Window – This is where your data is visualized. Note that the order of display in this window is the same as the vertical order of listing in the Table of Contents.
• Data View Tools – Quick access to many of the most often used tools for navigating and interacting with data in ArcMap
• Main Menu – Just what it is called. This is the typical Windows Main Menu, with some tools that are familiar, and some that may not be.

Getting Started

Visibility & Order of Display

1. Locate the Area_of_Interest Layer, in the Table of Contents, and click on the checkbox to turn on the layer’s visibility.
   
2. RepeatStep 1 for the Natural_Diveristy_Database_Areas, New_Haven_Water_Bodies and ned_elev Layers.
   
3. Notice that the Area-of_Interest Layer seems to have disappeared from the Map Document Window.
   
4. Click-Hold-and-Drag the Area_of_Interest Layer to the very top of the Table of Contents, releasing it when it is above the New_Haven_Streets Layer.
   
5. Notice that the Area_of_Interest Layer‘reappears’ above the other layers, reflecting its position in the Table of Contents.
   
6. In the Table of Contents, Right-Click on the Area_of_Interest Layer and Select ‘Properties’ from the context menu.
   
7. Select the ‘Symbology’ Tab (if it is not already).
   
8. Click on the Symbol Button to Open the Symbol Selector.
   
9. Use the Symbol Selector to change the File & Outline Colors to Yellow.
   
10. ClickOK twice to Apply the changes.

Navigation in Data View

1. Right-Click on the Area_of_Interest Layer and select Zoom to Layer.
   
2. To return to the previous view, Click on the Previous Extent Button, which works like a web browser’s Back Button.
3. Select the Zoom Tool Button and Drag a box across the upper-right are of the Map View, where the large body of water is.
   
4. Now Click on the Full Extent Button. This tool will zoom to the largest extent of the data in your map document.
   
5. On the Main Menu, change the Map Scale in the Scale Drop-Down Menu to ‘1:24,000.’
   
6. Select the Pan Tool Button and use this tool to position the Area_of_Interest box at roughly the center of the Map View.
   

Working with Layer Properties

You have already used the Layer Properties box to change the Symbology of the Area_of_Interest Layer, now you will use the same dialog box to change other things about the way your data is displayed.

Altering Symbology

1. In the Table of Contents,Right-Click on thened_elev Layer and Select‘Properties’ from the context menu.
   
2. Select the ‘Symbology’ Tab (if it is not already).
   
3. Click on the Symbol Button to Open the Symbol Selector.
   
4. UseColor Ramp Drop-Down list to change the color of this layer. If necessary, check the “Invert” box, so that the higher elevation values are represented by the lighter tones.
   
5. ClickOK to Apply the changes.

Labeling Features

1. Right-Click on the New_Haven_Streets Layer and SelectProperties from the Context Menu.
   
2. Click on the Labels Tab to bring it to the front of the window.
   
3. Check the “Label features in this layer” box.
   
4. Note the other options for altering the look of labels (but leave the default settings for now).
   
5. ClickOK to Apply the change.
   
6. Right-Click on the New-Haven_Streets Layer and SelectLabel Features from the Context Menu.

Note that the labels you just enabled have now been turned off. You could have simply used the context menu to turn on the label for this layer, since the Field the layer uses for labeling is called “FENAME” and ArcMap is fairly good at guessing what field to label with. When the labeling field is not so obvious, you should use the Properties Dialog to assign the correct Label Field, as shown above.