esri_to_sgdf            Convert a base64-encoded gzipped Esri ASCII
                        grid to an object of class SpatialGridDataFrame
get_stops               Extract walking times to nearby public
                        transportation stops
isochrone               Issue a walkalytics isochrone query
isochrone_esri          Issue a walkalytics isochrone query
isochrone_png           Issue a walkalytics isochrone query
isochrone_pois          Issue a walkalytics isochrone query
pixel_walktimes         Extract pixel-accurate walking times from
                        walkalytics raw data isochrones
pois_walktimes          Extract walking times to points-of-interest
pubtrans_ch_nearby      Issue a walkalytics pubtrans query
save_png                Save a base64-encoded PNG to file
