In the GeoJSON section, we illustrated that data properties are often part of the geographic data. The topojson command gives you the ability to filter out the ones you are not interested in, as well as provide a better naming convention to the ones you do want to keep. These capabilities are in the -p flag and passed to the command. For example:
topojson -o spain-topo.json -p name=ISO -- ESP_adm0.shp
We will create the TopoJSON file, remove all properties except ISO, and rename the ISO property to something easy to recognize. You can address multiple properties by comma-separating the list:
-p target=source,target=source,target=source