Visitor location is really basic / important so can I suggest that this should be part of the piwik core instead of requiring the aggravation of installing plugins? I have activated the GeoIP plugin but am still not getting accurate location info, as mentioned here.
We are working on it for Piwik 1.6: geolocation in core. stay tuned
Good news: GeoIP is now integrated in Piwik, enabling Accurate Visitors Geolocation in your Analytics reports. To enable GeoIP go to the Settings > Geolocation admin page, and follow the short instructions.
You can also get an even more accurate Country & City Database from here to enjoy top accuracy in detecting your visitors locations.
See also the documentation about Geolocation - Analytics Reports in Piwik.