The GPS antenna is in the top of the camera, above the lens. It's GPS only, no cell or wifi location, so it needs a view of the sky and won't work inside. There's three software GPS modes: entirely off, on when taking photos, or GPS tracking even when the camera is off. A warm start seems to find a position fix in 5–40 seconds. GPS location is written into EXIF tags in the photo and both Lightroom and Flickr understand the GPS format perfectly. There's no dedicated camera display of GPS data although you can see photos' locations in the viewer.

Digging deeper, exiv2 identifies 12 GPS tags in the JPEG and CR2 photo files. GPSVersionID is 2.3.0.0, there's lat/lon, altitude MSL (geoid corrected), timestamp, and minimal GPS status. Unfortunately location accuracy doesn't seem to be logged in the EXIF.

The GPS tracker is a nice bonus feature, I could see it being useful to document a photoshoot (although one wonders about battery life). Tracks are in standard NMEA format as a text file on the SD card. One fix is logged every 65-90 seconds. Each fix is logged both as GPGGA and GPRMC, basic position data. GPGGA includes HDOP and number of satellites and GPRMC includes speed and track. Note that as documented, the camera won't write GPS tracks to an Eye-Fi card but a standard SD card is no problem. Here's a sample log of me walking to lunch, see it mapped here. The track the S100 recorded is roughly accurate but missed logging my actual destination; compare to my AMOD dedicated tracker for the same walk. I'm pleased the S100 was able to log even when in my leather camera case on my belt.

The S100's GPS is a great addition to a great camera. It's not going to replace a serious GPS for navigation or technical measurements. But it's good enough for photos and terrific at making it easy to remember where you took your outdoor pictures.