Outputting JSON with reduced floating point precision

datasette-leaflet-geojson outputs GeoJSON geometries in HTML pages in a way that can be picked up by JavaScript and used to plot a Leaflet map.

These geometries often look something like this:


Decimal_degrees: Precision on Wikipedia says that 0.00001 should be accurate to within around a meter.

Shortening these floating point representations can shave 100KB+ off an HTML page with a lot of GeoJSON shapes on it!

There's a lengthy Stack Overflow about this but it's difficult to follow because ways of doing this changed between Python 2 and Python 3. Here's what worked for me:

def round_floats(o):
    if isinstance(o, float):
        return round(o, 5)
    if isinstance(o, dict):
        return {k: round_floats(v) for k, v in o.items()}
    if isinstance(o, (list, tuple)):
        return [round_floats(x) for x in o]
    return o

data = json.dumps(round_floats(data))

See issue 11 for details.

Created 2020-08-21T21:19:26-07:00 · Edit