Mapping US Census Bureau Data With ArcGIS Online
The US Census Bureau collects a vast array of demographic and economic data on a continual basis. Much of that data at various scales is made available through tables that can be downloaded from their data.census.gov data portal.
The challenge with that data is that it is made available to the public in formats that are difficult to import into GIS software.
This tutorial describes how to create choropleths of demographic data from existing layers in ArcGIS Onlin, and how to create new layers by joining US Census Bureau tables with TIGER/Line shapefiles for state, county, and census tract boundary polygons.
The US Census Bureau and the American Community Survey
Demographic data is "the statistical characteristics of human populations (such as age or income)." Etymologically, the word is a combination of the Greek words dêmos (people) and graphein (write) - literally, writing about people (Merriam-Webster 2020). Typical demographic variables for an area include:
- Median Household Income
- Median Age
- Median Family Size
- Percent of Residents With a College Degree
- Percent of Residents That Were Born Outside the USA
- Percent of Residents That Are Military Veterans
The US Census Bureau (USCB) is the part of the US federal government responsible for collecting data about people and the economy in the United States. The Census Bureau has its roots in Article I, section 2 of the US Constitution, which mandates an enumeration of the entire US population every ten years (the decennial census) in order to set the number of members from each state in the House of Representatives and Electoral College (USCB 2017).
Among the Census Bureau's many programs is the American Community Survey (ACS), an ongoing survey that provides information on an annual basis about people in the United States beyond the basic information collected in the decennial census. The ACS is commonly used by a wide variety of researchers when they need information about the general public.
Unlike the constitutionally-mandated decennial census which is only taken every ten years, the ACS continuously surveys people in America's communities so that the ACS data can be more detailed and current than the decennial census. However, because it is a survey rather than a complete count like the census, there is uncertainty about how accurately the sampling represents the facts on the ground, and that uncertainty is expressed in a statistical margin of error (MOE) on most ACS values (US Census Bureau 2018).
ACS data is released with data that is gathered over 1-year and 5-year intervals. The shorter intervals are more current, but less accurate. The longer intervals are more accurate, but less current. You should choose the data set based on whether the analysis you are performing needs data that is more accurate or more up-to-date. For this tutorial, we go with accuracy by choosing the most recent five-year estimates.
Community Profile Pages
If you are looking for quick information on a state, county, city or community, the USCB provides profile pages in data.census.gov that include basic demographic information about population, income, education, etc.
You can access a profile page by typing the name of the area of interest into the search bar and waiting for it to autocomplete. If there is a profile page, a link to that page will appear for you to select.
For areas that do not have profile pages (like ZIP Codes), searching the portal will give you links to tables where you can find information on that area.
Living Atlas Layers
ESRI, the company that provides ArcGIS Online, provides data as part of the service they sell to their users. One set of data from a wide variety of sources is their Living Atlas of the World. One of those data sources is the American Community Sources.
One challenge with using Living Atlas layers is that they are oriented around mapping in ArcGIS Online with with limited capability for analysis or for customization of symbology. However, if all you need is a quick map and you're just looking for common variables, the Living Atlas may be what you need.
This example shows how to create a quick choropleth of median household income. Note that with aggregated income numbers, median is often used instead of a mean (average) because income is unually not evenly distributed across a population, and a handful of wealthy people can distort averages so they are not representative of the typical economic well-being of people living in a particular area. (Yates 2020).
- Create a new map in ArcGIS Online.
- Select Add -> Browse Living Atlas Layers.
- Search for the data by name, in this case median household income.
- Zoom in on the area you want to display. This particular layer is a scale-dependent layer that changes the types of areas displayed depending in how closely you are zoomed in to an area.
- Change the transparency to 50% so you can see the geographic context for your data.
- Save the map under a meaningful name and share it to get a link.
You can get metadata on the source of the information in a layer by clicking on the ellipsis beside a layer and selecting Show Item Details. In this case, we find this data is actually provided by demographers at ESRI rather than the US Census Bureau.
Users in ArcGIS Online are part of an organization. This organization is associated with the business, government agency, or educational institution that holds the ArcGIS license that you are using.
If you are part of an organization where someone has created a demographic data layer, you can create a map from that layer fairly easily. This is especially useful for data sets where you will be using analysis tools on the data, where you wish to control the symbology of the layer more carefully, or if you need a variable that is not available from a source like the Living Atlas.
- Search for the layer in My Organization. For this example we use some ACS data uploaded to the organiztion in a layer named Minn 2017 American Community Survey ZIP Code Tabulation Areas (ZCTA).
- Style the layer and select the variable you wish to display. For this example we use median monthly rent.
- If needed, change the color ramp and/or adjust the scale to accentuate the differences.
- Change the transparency to 50% so you can see the geographic context for your data.
- Save the layer under a meaningful name.
- Share the map to get a link.
You can get metadata on the source of the information in a layer by clicking on the ellipsis beside a layer and selecting Show Item Details.
Finding A Location in Google Maps
There may be occasions where you want to find a location from an ArcGIS Online map in Google Maps, such as to find a neighborhood name or information about a neighborhood business.
- Use the Measure -> Location tool to find the latitude and longitude in ArcGIS Online.
- Paste those coordinates into the search bar in Google Maps.
Mapping Downloaded Table Data
It is possible to map table data that you personally download from data.census.gov, although the process involves multiple steps that are fraught with potential points for failure. You will generally want to avoid this process unless absolutely necessary.
Download The Data Table
- Search for the data you want in data.census.gov. For this example, we will map median gross monthly rent from the American Community Survey.
- When the table displays, select Geography and select the geographic areas you plan to map. In this case, we choose counties in NY State.
- Download the table. It is provided in a .zip archive file which you should open using the Windows File Explorer or whatever .zip file extraction tool you have available on your computer.
- Copy the .csv file that has data in the name to your desktop and open that file in Excel.
- Remove the top row in the file so that there is only one header row in the table before the data rows start.
Add The Data As an ArcGIS Online Bubble Map Layer
- Create a new Map from your ArcGIS Online home page.
- Select Add, Add Layer From File with the .csv data file.
- When asked to Locate Features, look through the fields and make sure the column containing the names of your areas are marked accordingly. In this example, the geographic areas should be marked as County.
- Select the column to style the bubbles. In this case we need to choose the monthly rent column.
Download a TIGER Polygon File
- Go to the TIGER Cartographic Boundary Files download page.
- Download appropriate file from the US Census Bureau's The 20m resolution files are good enough for a web map while being fairly small for quick upload. The download is a .zip file containing a shapefile of polygons you should save to your desktop.
- Add -> Add Layer From File with that downloaded .zip file.
Thematic maps indicate what is where. Data downloaded from data.census.gov data is the what. For bubble maps of states or counties, ArcGIS Online can geocode the place names in the data to get where. But for choropleths, you need where polygons that represent states, counties, census tract, etc. boundaries that can be colored with the what data.
A join is an operation where two data sets are connected to form a single data set. There are two kinds of joins: spatial joins and attribute joins.
A spatial join joins two data sets based on a spatial relationship. In the animation below, data from a points data set (the join layer) is joined with a polygon geometries data set (the target layer) to create polygons with data from the join layer.
This type of join is useful for state data, where ArcGIS Online can geocode American FactFinder data state names into points, and that point data can then be joined with state boundary polygons to create choropleths.
An attribute join connects two datasets based on common key values. This type of join is useful for county and census tract data, since ArcGIS Online cannot reliably geocode county or census tract names.
Spatial Join the Bubble Layer To The Polygon Layer
Because we now have a polygon layer and a bubble layer, we can perform a spatial join.
- Click the Analysis icon on that polygon layer and select Summarize Data, Join Features
- Since the data points are already geocoded, you can use a spatial join with Choose a spatial relationship
- Click off current map extent so any features not currently displayed (like Alaska and Hawaii) are included in the output data
- Save the joined data under a meaningful name
- Show credits to make sure the operation will not use too many credits. State joins should use under one credit
- The join may take awhile depending on how many features you are joining. If the join takes longer than five minutes, the tool may have completed without notifying you. You can return to the home page, return to the map, and then add the layer from your content.
- Style the polygons based on the newly joined data variable
Save and Share
Save the map under a meaningful name and share with everyone to get a link you can e-mail or submit for an assignment.
Note that you may get a warning message that one of your map layers also needs to be shared so the map is visible to everyone.