Working with road data has many areas to watch out for and one of these is invalid geometry. Our source data is OSM and is, therefore, collected by a community of users that are not trained by GIS professionals, resulting in errors. To execute spatial queries, the data must be valid or we will have results with errors or no results at all.

PostGIS includes the ST_isValid() function that returns True/False on the basis of whether a geometry is valid or not. There is also the ST_isValidReason() function that will output a text description of the geometry error. Finally, the ST_isValidDetail() function will return if the geometry is valid along with the reason and location of the geometry error. These three functions all accomplish similar tasks and selecting one depends on what you want to accomplish.