Search_API_Location module provides the Geo-spatial search experience to Drupal. Geo-spatial search mainly refers to searching data that is associated with a particular location. Currently only D7 supports this feature.
Queries such as give me all the restaurants that serves meat within 20 miles from me, or create a distance heat map of them are examples of spatial search. Here, some live websites like Airbnb, TripAdvisor , Yelp, Olx, etc. use geo-spatial searching functionality with different type of features which you can achieve using Drupal search_api with search_api_location and other extensions.
Spatial queries are complex database queries which differs from normal SQL queries as it deals with Big-data, because every object on the earth has its own coordinates and various problems that have to be faced in processing Big-data are capturing the data, storage, search, sharing, transferring, analysis, complex operation etc.
Technically Search_API_Location module is an extension for Search_API module and it mainly does two things i.e. adds support for indexing location values & helps in filtering and sorting location values