Reduce coordinate precision to 4 decimals

[perfectly-preserved-pie]

Attempting to reduce GeoJSON size by reducing the precision of the coordinates.

https://gis.stackexchange.com/questions/8650/measuring-accuracy-of-latitude-and-longitude

Using these ideas we can construct a table of what each digit in a decimal degree signifies:
The sign tells us whether we are north or south, east or west on the globe.
A nonzero hundreds digit tells us we're using longitude, not latitude!
The tens digit gives a position to about 1,000 kilometers. It gives us useful information about what continent or ocean we are on.
The units digit (one decimal degree) gives a position up to 111 kilometers (60 nautical miles, about 69 miles). It can tell us roughly what large state or country we are in.
The first decimal place is worth up to 11.1 km: it can distinguish the position of one large city from a neighboring large city.
The second decimal place is worth up to 1.1 km: it can separate one village from the next.
The third decimal place is worth up to 110 m: it can identify a large agricultural field or institutional campus.
The fourth decimal place is worth up to 11 m: it can identify a parcel of land. It is comparable to the typical accuracy of an uncorrected GPS unit with no interference.
The fifth decimal place is worth up to 1.1 m: it distinguish trees from each other. Accuracy to this level with commercial GPS units can only be achieved with differential correction.
The sixth decimal place is worth up to 11 cm: you can use this for laying out structures in detail, for designing landscapes, building roads. It should be more than good enough for tracking movements of glaciers and rivers. This can be achieved by taking painstaking measures with GPS, such as differentially corrected GPS.

I think an 11m spread should be good enough but I could drop down to 1.1m if needed...