see: http://bost.ocks.org/mike/map/

brew install gdal
npm install -g topojson

download: http://www.naturalearthdata.com/http//www.naturalearthdata.com/download/50m/cultural/ne_50m_admin_1_states_provinces_lakes_shp.zip

$ ogr2ogr -f GeoJSON -where "sr_adm0_a3 IN ('USA')" states.json ~/Desktop/ne_50m_admin_1_states_provinces_lakes_shp/ne_50m_admin_1_states_provinces_lakes_shp.shp
$ topojson -o states.json world.json