I had to build / maintain source code for a company that behaved in a very similar way as Uber. The company abandoned the source code, and we had to depend on other companies services to get it all working. The mapping software seemed like the hardest problem to solve as roads are ever changing, new housing complexes going in, zip code changes, etc. Of course geohashing is a thing now, and/or integration with google maps could work. Finding available drivers is a fun problem to solve... I dunno.