Let two great plugins play great together. Use FeedWordPress to aggregate geodata generated by GeoMashup.
FeedGeoMashup lets FeedWordPress pass GeoRSS data to GeoMashup. Starting with v2.0 you will find plugin options integrated into the FeedWordPress Admin UI. In particlar, you can set site-wide and feed-specific preferences to filter out posts that do not include GeoRSS data. You must have installed, activated and configured both FeedWordPress and GeoMashup.
VERY IMPORTANT: You must additionally configure FeedWordPress to "Expose syndicated posts to formatting filters." Do this on the admin side at: Syndication > Posts & Links > Formatting > Formatting filters.