Geospatial Data in Tableau comes in two primary forms namely: geographic fields and spatial data files.
Geographic fields can be assigned to fields in any source as long as field types and roles are assigned correct. Location fields are recognized by Tableau automatically like Country, State, City, Zip Code and so on. Most Geospatial fields will auto assign as long as the names are close and it could also be assigned manually. All Geospatial fields are string dimensions, except for Longitude and Latitude which are number decimal measures. It is important that data types are correct before converting them into geographic roles.
Spatial data files are special file types that contain data using geometry fields like Shape, GeoJSON and so on. They can also be produced by propriety tools or ETL (extract, transform, load) tools such as Alteryx and others.
Latitude and Longitude fields are automatically generated with standard location fields. This means that when a location field is selected the Latitude and Longitude will automatically appear in the rows and column.
Customizing Territories
Users can also Customize Territories allow users to dynamically select or consolidate geographic areas using Tableau's grouping functions. This allow non-standard geographic grouping to replace standard geographic fields. Here are the steps:
- Create a group of geographic field with select tool
2. Remove other geographic fields except the new group and the visualization will automatically group these. Polygons will form around the defined areas that were chosen in the group.
3. Remove 'State' from the Mark's card and then group will be combined into one piece and the rest into another. The group can also be renamed through 'Edit Alias' function.
Common Mapping Issues
Issues can occur when data contains unknowns or ambiguous spatial points. Here are some reasons like, a location can be abbreviated or misspelled, they could also be truncated zip codes and ambiguous locations could exist in multiple places (same city names but different countries). And there are different options to correct these issues.
Edit locations are used for adding fields to help Tableau identify location or define the Latitude and Longitude. Filter data are used to filter out ambiguous Latitude and Longitude points. But use this option with caution, unless you're certain these data points should be removed. Another option is Show data at default position (not recommended) which will result to the generic point of the ocean or the 'Null Island', where Tableau places unknown values. Zip codes are often the cause of nulls, so make sure to code them as string and pad zeroes if possible.