workingWithMapData.md

Map Data for Beginners

Data Formats

• Shapefiles

• *.shp
• *.shx
• *.dbf
• *.prj
• *.cpg

• Geotiff

  • *.tiff

• GeoJSON (Geographic JSON)

• TopoJSON (Topographic JSON)

• KML (Keyhole Markup Language)

Developed for use by Google Earth. Keyhole Markup Language is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers.

• GPX (GPS Exchange Format)

  GPX is an XML schema designed as a common GPS data format for software applications.

  • *.cpg

• WKT (Well Known Text)

Well-known text is a text markup language for representing vector geometry objects on a map, spatial reference systems of spatial objects and transformations between spatial reference systems.

Tools

• CSV -> GeoJSON
• WKT -> GeoJSON
• KML/GPX -> GeoJSON
• -> TopoJSON
• GDAL

Let's convert some data

shp -> json

❯ brew install gdal

❯ which ogr2ogr

❯ ogr2ogr -f GeoJSON us_states.json cb_2016_us_state_20m.shp

❯ topojson -o us_states_topo.json --id-property GEOID --properties name=NAME us_states.json

shp -> geojson

csv -> geojson

<OGRVRTDataSource>
    <OGRVRTLayer name="source">
        <SrcDataSource>/PATH/TO/source.csv</SrcDataSource>
        <GeometryType>wkbPoint</GeometryType>
        <LayerSRS>WGS84</LayerSRS>
        <GeometryField encoding="PointFromColumns" x="LONGITUDE COLUMN HERE" y="LATITUDE COLUMN HERE"/>
    </OGRVRTLayer>
</OGRVRTDataSource>

❯ ogr2ogr -f GEOJson geo_result.json source.vrt