Location is specified using Atom 1.0's official extension mechanism (see Extending Atom). We add a <georss:where> element as a child of the <entry> element. Within <georss:where> you may specify geography. We recommend that the GML encoding is used as follows:
GeoRSS Simple could also be used:
Atom processing software is required to either read or ignore this type of "foreign markup"--not fail, so there is no danger of breaking someone's RSS reader (or publisher) by including this <where> element in your feed.
NOTE: GML allows you to specify a coordinate reference system (CRS) other than WGS84 decimal degrees (think lat/long). If you have a need to express geography in a CRS other than this, we recommend that you specify the geographic object multiple times, one in WGS84 and the others in your other desired CRSes.
for now see the examples on the GML page