For very precise mapping I use:
http://kismac.de/
Will you drive around, KisMac use your GPS and Signal strength to find the exact location of the Hot-Spot. You can even download map directly with KisMac and map all the hot spot and trace everywhere you went. Very Nice. If you have third party WI-FI card, you can do a lot more but I don't use those functions.
I also bought iStumbler
http://www.istumbler.com/
They just came out with a new version.
I have downloaded Coconut Wi-Fi and I will try it soon.
Franco