[GIS] How to reduce the file size of GeoJSON data

geojsonogr2ogrtigertopojson

For my project I am trying to convert the tiger shapefile information for us states into GeoJSON format

However when I use the ogr2ogr tool the data file is about 20 MB. I have seen the geoJSON file of US States elsewhere of around 88KB.

How do I reduce the output to geoJSON file?

Best Answer

You have two ways of reducing the file size:

Remove all the pretty formatting and redundant white space. In some 'XML-style' files this can be a surprisingly large amount and can easily double or even treble your file size. However I doubt it accounts for the difference in your volume and the data you link to above.
Reduce the volume of actual data either by reducing your coordinate precision (e.g. 6 decimal places vs say 12) and/or reducing the actual number of vertices representing the features in your data. I suspect that this accounts for a substantial proportion of the difference in file sizes you are seeing. Much depends on your use-case for how much simplification will be acceptable and only you can decide that.

Related Solutions

GeoJSON – How to Validate GeoJSON Files

5 months late, but I made this thing that should help http://geojsonlint.com/.

[GIS] Converting UTM to Lat/Long with a geoJSON file in pyproj

This should do the trick. I haven't been able to install the pyproj module, but at the point marked #do transformation. I tested it by doing simple arithmetic. I put in the function based on your code. Basic structure is:

Load data from file.
Traverse json string - essentially nested dictionaries and lists
Iterate through the coordinates. The coordinate lists are heavily nested to allow for multipart polygons
Write altered data to a new file

Code:

import pyproj
import json

#define projections
wgs84 = Proj('epsg:4326')
IrishGrid = Proj('epsg:29902')

#load in data
with open(r'path_to_file_you_want_to_edit.json', 'r') as f:
    data = json.load(f)

#traverse data in json string
for feature in data['features']:
     #print feature['geometry']['type']
     #print feature['geometry']['coordinates']

    #all coordinates
    coords = feature['geometry']['coordinates']

    #coordList is for each individual polygon
    for coordList in coords:

        #each point in list
        for coordPair in coordList:
            print coordPair
            x1 = coordPair[0]
            y1 = coordPair[1]
            lat_grid, lon_grid = numpy.meshgrid(x1, y1)
            #do transformation
            coordPair[0],coordPair[1] = pyproj.transform(IrishGrid,wgs84,lat_grid, long_grid)

#write reprojected json to new file
with open('path_to_new_file.json', 'w') as f:
    f.write(json.dumps(data))

Hope this helps.

Best Answer

Related Solutions

GeoJSON – How to Validate GeoJSON Files

[GIS] Converting UTM to Lat/Long with a geoJSON file in pyproj

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