Limit GeoJSON to coordinate precision of 7 (not 15)

[nvkelso]

From a Twitter support request we're currently exporting too much precision in our GeoJSON files for Metro Extracts.

• https://twitter.com/jestferfun/status/895381713391542272
• https://twitter.com/jestferfun/status/895381844178354176

Reviewing the support request it looks like we export default of 15 coordinate precision now when 7 is plenty. This will result in smaller file sizes, a win for everyone – and the original OSM data is accurate to 7 decimal places so we're not loosing precision.

The 15 precision is coming from OGR's GeoJSON driver defaulting to 15. But it's possible to set that to 7 two different ways:

• http://www.gdal.org/drv_geojson.html

COORDINATE_PRECISION = int_number: (OGR >= 1.9.0) Maximum number of figures after decimal separator to write in coordinates. Default to 15 for GeoJSON 2008, and 7 for RFC 7946. "Smart" truncation will occur to remove trailing zeros.
SIGNIFICANT_FIGURES = int_number: (OGR >= 2.1) Maximum number of significant figures when writing floating-point numbers. Default to 17. If explicitly specified, and > COORDINATE_PRECISION is not, this will also apply to coordinates.
RFC7946=YES/NO. (OGR >= 2.2) Whether to use RFC 7946 standard. Otherwise GeoJSON 2008 initial version will be used. Default is NO (thus GeoJSON 2008)

If we're using a newer OGR >= 2.2 then we should just say RFC7946=YES. If not then set one of the other flags (I think COORDINATE_PRECISION=7 but verify).

The code would need to be changed here for OSM2PGSQL:

chef-mapzen_odes/templates/default/shapes.sh.erb

Lines 28 to 36 in 7d6643b

	# generate geojson from shp files
	#
	if [ ${geojson} == 'true' ]; then
	ogr2ogr -lco ENCODING="UTF-8" -f GeoJSON -t_srs epsg:4326 shp/${slug}_osm_line.geojson shp/${slug}_osm_line.shp
	ogr2ogr -lco ENCODING="UTF-8" -f GeoJSON -t_srs epsg:4326 shp/${slug}_osm_point.geojson shp/${slug}_osm_point.shp
	ogr2ogr -lco ENCODING="UTF-8" -f GeoJSON -t_srs epsg:4326 shp/${slug}_osm_polygon.geojson shp/${slug}_osm_polygon.shp
	zip -j shp/${slug}.osm2pgsql-geojson.zip shp/${slug}_osm_*.geojson
	fi

And here for IMPOSM:

chef-mapzen_odes/templates/default/shapes.sh.erb

Lines 72 to 77 in 7d6643b

	if [ ${geojson} == 'true' ]; then
	for i in ${arr[@]}; do
	ogr2ogr -lco ENCODING="UTF-8" -f GeoJSON -s_srs epsg:4326 -t_srs epsg:4326 ${tmpdir}/${slug}_${i}.geojson ${tmpdir}/${slug}_osm_${i}.shp
	done
	zip -j shp/${slug}.imposm-geojson.zip ${tmpdir}/${slug}_*.geojson
	fi