We ended up using some random C library to parse the shapefiles into an easier to read text format of our own design, and then pulling them into packed binary f

We ended up using some random C library to parse the shapefiles into an easier to read text format of our own design, and then pulling them into packed binary files with an external index that we memory map in the code to maximize the speed. The system is all extremely custom and is highly optimized for write-once/read-many. Making even a tiny change to a single polygon means a full refresh that takes hours to complete.