What is a FlatGeobuf file?
FlatGeobuf is an open, binary vector format built on FlatBuffers. It stores features with a built-in spatial index, so software can read just the area it needs.
It is one of the fastest formats to read and write, and it can be streamed over HTTP from cloud storage without a map server.
What is a Shapefile file?
The Shapefile is Esri's vector format from the early 1990s. One dataset is a set of files — .shp (geometry), .shx (index), .dbf (attributes) and .prj (coordinate system) — usually shared as a .zip.
It is still the most widely supported GIS format, but it has hard limits: one geometry type per file, field names of up to 10 characters and a 2 GB size cap.