Joining an external table to a raster dataset in ArcGIS Pro is typically done by joining the table to the raster's attribute table (RAT). This process allows you to link additional descriptive information to the unique cell values within the raster.
Here's how you join a table to a raster attribute table in ArcGIS Pro:
To combine data from an external table with the information stored in your raster's attribute table (RAT), you use the standard table join functionality in ArcGIS Pro. This requires your raster dataset to have an existing raster attribute table, which is common for discrete rasters like land cover maps or classification results.
Understanding the Join
A join appends the attributes of one table (the join table) to another based on a common field (the join field) found in both tables. When joining to a raster attribute table, the RAT acts as the destination table, and your external table is the join table. The common field is usually the Value field in the RAT, which corresponds to the unique cell values, and a matching field in your external table.
Steps for Joining a Table to a Raster Attribute Table
The process in ArcGIS Pro is straightforward and uses the layer's context menu:
- Add the Raster Dataset: Ensure the raster dataset that has the raster attribute table you want to join to is added to your current map or scene in ArcGIS Pro.
- Access Joins and Relates: In the Contents pane, right-click the raster layer.
- Initiate the Join: From the context menu, point to Joins and Relates, and then click Add Join. This opens the Add Join geoprocessing tool pane.
- Configure the Join Parameters:
- Input Layer: The raster layer you right-clicked is automatically selected.
- Input Join Field: Choose the field from the raster layer's attribute table that contains the values you want to match (e.g., the default
Valuefield). This field is also referred to as the layer's join field. - Join Table: Select the external table or layer that contains the attributes you want to append to the raster attribute table.
- Output Join Field: Choose the field from the Join Table that matches the values in the Input Join Field. This is the join table's join field.
- (Optional) Keep All Target Features: You can choose whether to keep all records from the raster attribute table or only those that have a match in the join table. Keeping all is common for RATs.
- Validate and Run:
- Click Validate to check if the join fields have matching data types and values. This helps identify potential issues before running.
- Click Run to perform the join.
Once the join is complete, you can open the raster attribute table, and you will see the fields from the external table appended to it.
Here's a summary of the key parameters in the Add Join tool:
| Parameter | Description | Example (joining land cover codes to descriptions) |
|---|---|---|
| Input Layer | The raster layer with the attribute table. | LandCoverRaster |
| Input Join Field | Field in the raster attribute table to match on. | Value |
| Join Table | The external table containing the data to join. | LandCoverLookupTable |
| Output Join Field | Matching field in the Join Table. | Code |
| Keep All Target Features | Keep all records from the input layer (RAT). | Checked (usually desired for RATs) |
Note: The reference specifically mentions "Add the raster dataset... In the table of contents, right-click... Joins and Relates, then click Join. Choose the field...". These core actions are fundamental and directly map to steps 1-3 and part of step 4 in the ArcGIS Pro workflow described above.
Making the Join Permanent
By default, a join created this way is temporary and only exists within your ArcGIS Pro session or project. If you close and reopen the project, the join will be gone. To make the join permanent, you need to export the raster layer or its attribute table after the join is established:
- Right-click the joined raster layer in the Contents pane.
- Point to Data and click Export Features (if you joined to the attribute table directly or if the raster has a standard attribute table) or Export Raster (if you joined via the layer properties and want a new raster). Exporting the table to a new geodatabase table is often sufficient if you only need the joined table.
Joining tables to raster attribute tables is a powerful way to enrich your raster data with descriptive information, making maps and analyses more informative.
