In the previous lesson, you downloaded tabular data, explored it, and created a new table. In this lesson, you'll use ArcMap to perform a table join, which takes data from one table and connects it to another table. In this case, you'll join your Homeless Data table to the attribute table of a map layer of the United States.
Add a layer from ArcGIS Online
The geography of your homeless data is the state level of the United States, so you'll need a layer of the United States to appropriately map your data. You can add one to your desktop software from ArcGIS Online.
- Start ArcMap.
If you don't have ArcMap, you can get it by purchasing ArcGIS Desktop from the Esri Store.
The ArcMap - Getting Started window opens. This window allows you to open previous maps or map templates.
- Close the ArcMap – Getting Started window to start a blank new map.
- On the Standard toolbar at the top of the screen, click the arrow next to the Add Data button and choose Add Data From ArcGIS Online.
If this option is not available to you, you can add it by following these instructions.
- In the ArcGIS Online window, type USA State Boundaries into the search box and press Enter.
If you're signed in to an ArcGIS organizational account, you'll search only for content within your organization by default. To search all content on ArcGIS Online, uncheck the Only search in (my organization) box.
- In the results, find the USA States (Generalized) layer by esri_dm and click Add.
The layer is added to the map.
- In the Table Of Contents, right-click USA_States_Generalized and choose Open Attribute Table.
The attribute table opens.
The attribute table contains data describing the features of the layer. Some of the fields in this table include the state name (STATE_NAME), the region of the country the state is in (SUB_REGION), and the state's abbreviation (STATE_ABBR). The field containing state abbreviations has identical data to the State column in your Homeless Data table.
- Close the attribute table.
The attribute data can also be accessed from the map with the Identify tool.
- On the Tools toolbar, click the Identify tool.
- On the map, click the state of North Dakota (located in the north-central part of the country) to open the Identify window.
The Identify window contains the attribute information for North Dakota. Selecting any other state will bring up that state’s information. The attributes of a layer are associated with map features, so you can use attribute data to change map symbols—perfect for presenting data both visually and geographically.
- Close the Identify window.
- On the Standard toolbar, click the Save button.
- Save your map as Homeless Map.mxd in the Homeless Project folder you created in the previous lesson.
Next, you'll join your homeless data to the United States layer's attribute table.
Join the homeless data to the layer
A table join takes data from one table and connects it to data from another. You can't just join any two tables; both tables must share a field of common values. Otherwise, the software won't be able to identify which records in the join table match which records in the target table. In this case, the tables you want to join have common records of state name abbreviations.
- Right-click USA_States_Generalized, point to Joins and Relates, and choose Join.
- In the Join Data window, for the first setting, choose STATE_ABBR as the field to base the join on.
- For the second setting, click the Browse button next to the menu.
The Add window appears. By default, the window shows the contents of your map's Home folder, which is the folder where the map document is saved. Because you saved your map in the Homeless Project folder, you should see the contents of that folder in the Add window.
If the window does not show your map's Home folder, you can navigate to the Home folder by clicking the Go To Home Folder button at the top of the Add window.
- Double-click Homeless Data.xlsx and double-click Sheet1$ (the first sheet in the table) to select it as the table to join.
- For the third setting, confirm that State is selected.
- At the bottom of the Join Data window, click Validate Join.
Validate Join tests whether the join will succeed. If both tables have valid field names, the join will be validated.
- Close the Join Validation window and click OK to join the tables.
- Open the attribute table for USA_States_Generalized.
Four fields are appended to the table: State, Change, Pop13, and Homeless13.
Although the raw data is the same as in your spreadsheet, the numbers are formatted differently. The Pop13 and Homeless13 data is missing comma thousand separators, and the Change data is displayed as a decimal instead of a percent. After you publish your layer to ArcGIS Online, you’ll reformat the data, but for now, confirm that the fields have been added.
- Close the attribute table.
- Save your map.
In this lesson, you joined your data to a layer of the United States. In the next lesson, you'll prepare your joined data for publication and publish it to ArcGIS Online.