rs the opportunity to redraw the existing map more accurately.
Things to watch out for
Sometimes photographs are displaced away from the real position of the features that are photographed. You should check that the roads in the photograph are aligned with the GPS tracks that people have contributed to OSM and move the background if you need to.
Something else to watch out for is features that have changed on the ground since the photographs were taken. It is best to use local knowledge alongside the pictures to avoid this.
You can redraw roads with more points on curves to follow the road on the ground and you can also straighten roads that really are straight. You can also look for roads with markings dividing the lanes and tag them suitably; check for tagging advice in your country but this often means highway=tertiary or above when more than a short stretch near junctions is marked.
High-resolution imagery is one of the few practical options for mapping Buildings. Since each town and city could have thousands of buildings, you'll need to decide where you want to start. Maybe doing all the buildings for organizations such as churches, schools, community buildings. Maybe you start with the downtown or a major shopping centre. If you want to tackle a whole town, try to focus on the larger buildings and work one a specific area at a time. Aerial imagery is not always up to date, so you may have to rely on your own notes or memory to image some of the newer buildings.
When photographs are taken at an angle the tops of buildings (especially high ones) are a distance away from their correct position. You can move the traced outline of the building so that it is aligned with the base of the building on the sides where you can see it. For some tips how to draw buildings, see Roof modelling.
Main article: Points of interest (POI)
GPS receivers make it very easy to mark waypoints. On the Geko for example, "Mark", "OK" will insert a numbered waypoint. In the example shown, the cartographer stopped in a pub car park, and marked a waypoint which was stored as number 206. Some GPS models allow you take an 'average' point. This will take multiple GPS points and then average all the points, in theory creating a more accurate waypoint. Usually this is used when accuracy is higher priority with the data collection and time isn't as much as a factor but this can still be done quickly.
Use a notepad, or dictating-machine, to record what that waypoint corresponds to. Although it's usually possible to type this information into the GPS itself, it can be very fiddly.
For special needs you may want to upload the waypoints to the osm traces server.
GPS Offset Method
(Intermediate Level Technique)
When there is a structure or object that you want to GPS but is inaccessible (like a cell tower surrounded by a large fence) then you can use the 'GPS Offset Method' to get its coordinates. To do this you will need your GPS, compass, optionally a range finder and a way to record your data like a notebook or voice recorder. (Instead of using a range finder you can just estimate the distance but this will usually be less accurate.)
- Start collecting GPS points for your waypoint and give it some kind of recognizable ID like CT1 (Cell Tower 1). This is a good opportunity to use the average waypoint feature (that is included in a lot of GPS units) since the next steps will take a minute or so to complete.
- Use your compass to sight the structure and then record the bearing (azimuth) from your current location to the structure in your notebook.
- If you have a range finder, shoot the structure and record the distance to it in your notebook. Estimate the distance if a range finder isn't available.
- End GPS data collection and save your waypoint.
An example format to record this information in your notebook:
- CT1 = 90m @ 340° from WP1
- CT2 = 60m @ 176° from WP2
When you get back to your computer you can download your waypoints and enter your offset notes into a spreadsheet. For less accurate coordinates of these structures, you can use the measure tool 