Add columns to your attribute table based on common attribute values.
You can add you own data in various tabular formats (.dbf .xls .csv or other delimited text) to the attributes of a geographic layer (e.g., polygon, line, or point). You need to have a variable in your own data and one in the target GIS layers that have matching values (key columns) so that the program can match up the rows correctly (e.g., match a county name to a county name).
Right-Click method: Highlight the layer's name in the Contents Pane, right-click, choose Joins and Relates ... Add Join.
Geoprocessing pane: From the Analysis Tab in the Ribbon, click Tools to open the Geoprocessing Pane. Then search for the Add Join tool.
The Add Join tool adds all the columns from the join table to your target table. It is only a virtual connection between the tables: the attributes of the underlying files aren't updated. Only in the ArcGIS Pro Project is the connection being made.
If you want only selected columns added to the target table, or
if you want to actually update the target with the new columns (it's not just a virtual connection).
Find the Join Field tool by searching in the Geoprocessing Pane.
Numeric versus text fields
Special care must be taken with the variable definitions, especially when numerals are being used as codes, which should be text (string) variables -- e.g., ZIP Codes, ANSI (FIPS) codes. It's easy to strip leading zeros, for example, if you open a CSV file first in Excel.
String values must join to string values, and numeric to numeric. You can use the Table to Table tool to to control the field definition when you import the Excel or other tabular data into a file geodatabase table or .dbf table.
The added data comes from the attributes of another geographic layer, not from purely tabular data.
The join is based on the location of features in the layers, rather than on common values in an attribute field.
The result will be a new layer (i.e., a new shapefile) that includes the newly expanded attribute table. It doesn't alter the attributes of the original layer that you're joining to.
You might typically use this to determine the location of each point in a layer and associate each with the attributes (including geographic identifiers) of a geographic polygon (e.g., a census tract, whose attributes would include the number of the tract).
This geoprocessing tool can be accessed two ways.
Right-Click method: Highlight the layer's name in the Contents Pane, right-click, choose Joins and Relates ... Spatial Join.
Geoprocessing pane: From the Analysis Tab in the Ribbon, click Tools to open the Geoprocessing Pane. Then search for the Spatial Join tool. Also, it also may be one of the commonly used tools displaying in the Ribbon (Analysis Tab).
The Spatial Join tool lets you choose which columns from the join table to add to your target table.There are also options for summarizing values in cases where there are multiple join features joining to a target feature.