Split big topojson files into a grid of files

I made a script to split a giant topojson file into a ton of smaller ones.

Here’s the code: https://github.com/jakekara/toposplit

Why?

I needed to make a block-level map of the entire state of Connecticut. Here’s a demo of the final product. Click a town to zoom in. It loads only the topojson file for the grid it needs, on the fly, rather than loading the entire state’s worth of blocks at once.

mapshaper comes close but…

Census blocks are tiny – there are 65,000+ in Connecticut, and Connecticut is a tiny state. That means a topojson file, even simplified, of all the Census blocks in the state is 30+ MB. Waaay too big.

So I decided to split the state into a grid, make little topojson files for each grid, and load them on the fly.

Mapshaper has the ability to split a topojson file into layers based on a grid, but I needed to split those layers out into separate files so I wrote toposplit.

There’s some documentation in the repo, but I suggest running the demo script and seeing how that works to see how I actually used it. Instructions for running the demo are in the EXAMPLE section of the README.

The demo downloads a giant shapefile, splits it up into little ones…