there are many nav. apps. for android. the one that comes pre loaded on the s3 is navigon - by garmin. i will have a look later, but i don't use it often enough to be familiar with it.
there appear to be several walking nav. apps. for venice that sound like worth a try.
do you know exactly what you want to do?
ie. drive, walk, have points of interest show or track yourself???
also, will you only be carrying android? any apple?
