Distributed database for worldwide LIDAR point cloud
I have dealt with something very similar to this. This is quite a broad problem but I'll try to offer the pointers I can after a year (and then the rest) of dealing with massive geographic data sets.

I'm not saying "do these", I'm saying these ideas will be resourceful depending on your hardware situation and software needs. You clearly already have good ideas about distributing out the data, that's good.

Firstly, I'd make sure not to have monolithic tables with too many sets of datatypes. Normalise out - I've found that splitting your geospatial columns into an entirely separate table.

Secondly, write down the sort of queries you'd expect a typical client to need. There's a 'chicken and egg' situation here, but I always like to write the SQL then design the table and indexes around that. Rick James' blog (former DBA at Yahoo!) always has nuggets of wisdom on this.

Thirdly, shard by location, which you have already touched upon. You can try doing this by 5-10 degree boxes around the world by latitude and longitude, depending on how dense your data is. Or if your data density is not uniform around the world, try a more sophisticated approach based on densities.

Our approach to sharding involved creating multiple Amazon RDSs, and then having a meta data table that mapped a range to the correct database and table. This is a simpler approach if you have the cash - personally I was against this due to the spiralling costs, but the uptime of AWS is top-notch. Something for you to think about.

Good luck, sounds like a cool project!