In more detail
Phones usually write GPS coordinates into the EXIF of every photo unless location tagging is switched off. Coordinates are stored as degrees, minutes and seconds and can pin a picture to within metres. Shared files that keep their geotag can reveal where someone lives, works or travels. The EXIF GPS block holds latitude and longitude as three rational numbers each, plus a reference letter (N/S, E/W), and often altitude, direction and a UTC timestamp. Videos and some social apps store location in their own Metadata fields as well.
Why it matters
A photo of a new sofa sold online can give away the seller's home address, and holiday pictures posted in real time show that a house is empty. For investigators the geotag is a strong lead, but it can be edited or copied from another file, and phones sometimes record a stale or network-based position, so check it against what the image shows.
Example
A GPS block of 48° 51' 29.6" N, 2° 17' 40.2" E converts to decimal degrees as:
48 + 51/60 + 29.6/3600 = 48.858222
2 + 17/60 + 40.2/3600 = 2.294500
That is 48.858222, 2.294500, a point by the Eiffel Tower in Paris. South latitudes and west longitudes become negative. One second of latitude is about 31 metres, so the tenth-of-a-second precision here is roughly 3 metres. Strip location data before sharing with the EXIF Metadata Remover.