As far as I examined spatial search is based on coordianates comming from a source(database table or something else with the available information) and this being passed to lucene. To integrate this in sitefinity search and perform spatial searches the spatial data have to be integrated with sitefinity search. This is done by creating a custom search pipe that will query the datasource with spatial information and return search results.
is a blog post with a sample how to create custom search pipes and register them in sitefintiy.
and the related documentation
about sitefinity publishing pipes. Creating new search pipe will appear as search index option in Administration->Search.
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