Avoid "Mars probe" issues: as specified in Table 1, the units for <lat/> and <lon/> MUST be decimal degrees (where South and West are negative, North and East are positive), the units for <alt/> MUST be meters above or below sea level, and the units for <error/> MUST be arc minutes.
In applications where updates are sent whenever there is a certain distance change in location, those applications SHOULD account for time as well, to avoid rate-limiting when the user is (for example) on a jet plane. One possible way to do this would be to send updates at most once per minute of time (every time 60 seconds have elapsed).
Inferences SHOULD NOT be made about accuracy from the number of digits specified in the location or altitude.
-Why the datum madness? See <http://www.jabber.org/protocol/geoloc/gps_datum.html> for an example.
+Why the datum madness? See <http://www.xmpp.org/extensions/gps_datum.html> for an example.
An entity can provide a GPS path by publishing a series of items (i.e., multiple pubsub events) with appropriate values of the <timestamp/> element.