Geotagged photos and plan pins: when location data helps and when it misleads
Reviewing the week's deficiency photos, the project manager opens the map view and finds a cracked-tile photo placed in the middle of the street. A photo of a ceiling valve on level 4 sits on top of one taken in the parkade. Both photos are real, but their positions do not mean what they seem to.
A geotag is the phone's own estimate of where it was. Under open sky a smartphone is typically accurate to within a 4.9 m radius; accuracy gets worse near buildings, bridges and trees, indoors and underground, and where signals reflect off walls. A point on a map says nothing about the floor, and marks where the camera stood, not what it was pointed at. A geotag supports other records but proves little alone, and is only as trustworthy as the file that carries it.
Use each for what it does well
- Use the geotag for the rough place: which part of a large or linear site, or whether the phone was near the site at all.
- Check the accuracy figure, and where the position came from, if your app shows them; a position that may be off by more than the size of what you are recording cannot pinpoint it.
- Name the area inside buildings: building, level and area from the project's location list.
- Pin it on the current drawing where a few metres matter: a valve, a sleeve, a crack, a deficiency.
- Say which way you faced when the subject is across a street or a room: "from the east sidewalk, looking west at the north elevation".
- Question odd positions, such as a photo in the street, and fix them with an area and a pin.
- Keep the geotag after you pin a photo: with the pin and the capture time, it adds weight to the record.
Common mistakes
- Reading the map position as the location of the subject rather than of the phone.
- Treating a geotag as proof of where a photo was taken.
- Dragging a pin to where a photo "should" be without checking what it shows.
- Turning location off on site phones, and losing the rough position with it.
Checklist
Before you rely on a photo's location, check
- Where it was taken: open sky, or indoors, underground or beside tall buildings
- Whether a few metres would change the answer
- A named building, level and area
- A pin on the current drawing where the exact spot matters
- The direction the camera faced, in the description
- A position that makes sense, and other records that agree
Check your understanding
A photo of a crack in a level 3 slab has a geotag accurate to a few metres. Why is that not enough to find the crack again?
