reading large files with readArrayBuffer

i extracted my city's ways from openstreetmap. with some clever encoding (btw i laughed at Uint24Array but it's just what i needed) i'm actually below 200k. i'm amazed it's fast enough to display on the watch with little optimisations (1.5 secs to display). i still need to add the street names and port the low mem path algorithm to javascript and we might have a full gps. i'm not still 100% sure the path algorithm will fit the ram though, it's kind of a challenge. well, all the stuff i like.