Mapping Tricks and tips
|It has been proposed that this page be moved to "Surveying tips and tricks". (Discuss)|
This page collates tricks and tips regarding different mapping techniques that OSMers have experienced. It is intended only for regular mappers. For more expansive and more technical coverage of this area, see the main mapping techniques page.
Check memory and battery capacity before setting off
Always check your batteries and memory capacity on your GPS and your camera before starting out.
Make sure you have your memory card in place. Remember what you did last time? You took the memory card out of the camera/gps to upload the data. It's not still there is it? You'd be really embarrased if you switched on your camera/gps to start tracking & realised the memory card was still in the slot in your computer at home. So, as you walk out the door to set off on a mission look in the camera/gps unit & make sure the card is in the slot. It could also be useful to bring the cable for connecting the camera to your computer, so you can move files from memory card to your hard drive, freeing space in the camera. If using a laptop, consider disabling your screen saver, or at least, set it to a very long time. It is helpful watching the screen from time to time to see what you have already mapped, but you most likely won't use the keyboard or touchpad for periods beyond usual screensaver trigger time.
Got kids? They love digital cameras. Snap, snap, snap... 35 blurry pictures of the dog, 5 videos of the floor & running round the house. Does wonders for your memory capacity & the battery-you-thought-you-had-just-charged.
Let this be a warning to you...
Record track points at one second intervals
For best results in urban areas always record track points at one second intervals.
Stand still until you get a fix
For best results do not start moving until your GPS has a 3D fix.
Many GPS receivers can take much longer to get a fix if you are moving and can give really wacky results.
Stand still and wait until your GPS says that it has a good fix and even then it's probably a good idea to wait another 30 seconds or so for everything to settle down.
Always turn right (or left)
When recording tracks by bicycle in urban areas, a good way to cover convoluted housing developments is to always turn right (or, in the UK, always turn Left). It is easier to catch those elusive little side roads this way. It also avoids making turns across oncoming traffic which can be both dangerous and time consuming. Typically this means that you cover all the branch roads on one side of a main road on your outward journey and those on the other side on your return journey.
Arriving at a street you already have mapped, just turn around and go back. Arriving at a junction where you have been, do the following: take the most right free street you have not visited. This means if you cannot turn right because there is a track, go straight. If you cannot also go straight, go left. If you cannot go left turn around and drive back the way you came.
To map a large area, or a whole city, begin by driving all the main streets with the car. After this you have divided your city in chunks. Now you can choose a chunk, small for short trips, big for longer, and map it. The main streets already mapped are your borders. Follow the 'always turn right' tip within the confines of a border.
Prior region preparation for GPS-degraded operation
If you are of the kind that likes very accurate OSM maps even at small scale…
It is worthwhile to have some features exist in the OSM dataset prior to going out to go out and survey more. In certain places, the GPS accuracy is reduced and it may actually be more useful to just place a map marker in relation to another feature, completely foregoing the GPS signal.
An example might be mapping amenity=bench in a botanical garden with a lot of little footways and degraded positional accuracy. When surveying, you will recognize that a bench may be in the north-east corner of an intersection of two ways, so the GPX waypoint (a "note" for later) on a mobile device (running something like OsmAnd) should be placed, of course, in the north-east corner of the digital resepentation of the intersection, instead of whereever your GPS claims you are. Having an accurate network of footways already present is essential for this. Some armchair mapping off aerial imagery may assist in getting this footway network, and possibly better so than trying to ground-survey it.
Another example is shop discovery in a dense (say, European-style) city center. Here too, placing the GPX waypoint with shop details onto the right building and ignoring the GPS location — because that might show your location as being already at the next building — can turn out to be easy. That of course requires that the house numbers are already present in the digital dataset and at your disposal.
In cars, always take a passenger
The driver is only the driver. - The passenger has to take notes on street names, mark waypoints, and can tell the driver which streets he's already done (by looking at the GPS)
Capture several features in one photo
Post Boxes are often near Street Signs, so kill two birds with one stone by taking one photo of both the Street Sign and the Post Box. If you get lucky there'll be a phone box there as well.
Oh, and don't forget to mark them on the map with amenity=post_box and/or amenity=telephone.
Edit data as soon as possible after creating the tracks
Try to enter the street and other data as soon as possible after you have seen the area and created the tracks. You will remember more details that way. Also it is best to enter the data from your own tracks. Nobody knows better than you exactly what you did.
Use a camera to support your GPS tracks
- Main article: Photo mapping
If you have a digital camera use it to record information along the way as you create your tracks. Street signs and Points Of Interest (POI) especially. If you set the camera clock to the same as that of the GPS then you can match the images to the GPS tracklog. Take a picture of your GPS showing the time on it to help synchronise between the timestamp on the image and the tracklog timestamps.
Use a tape recorder or similar
- Main article: Audio mapping
It can be cumbersome to take many notes, especially when on a bike. Use a tape recorder or similar to record notes as you go. You can also mark waypoints on your GPS at the same time. You only have to record then things like: "Waypoint 15 is start of Summer Lane" or "Waypoint 21 is telephone booth on eastern side of street". Make sure to spell out streetnames when they have unusual spellings. See also JOSM hints for how to automate synnchronization with your GPS tracks and/or waypoints.
Be prepared to visit an area several times
Theoretically you could go out to an area, create your tracks, note down everything important, go home, enter all the data and be done with it. But it is very difficult to do that. There'll always be details which you forget. Be prepared to go through each area at least twice. In the first round make sure to get tracks for all roads and major footpaths etc. Also note down street names and all amenities etc. which you can get. Then enter all this data, print out a map and go back to compare the map with reality.
Hints for doing rail tracks
If you are going to a rail trip, get a fix before boarding. Once you get the fix, the ephemerides are valid for 2-4 hours and your receiver can get a fix in a matter of tens of milliseconds. This is valuable in harsh receiver conditions such as rail cabs. It can also help (though to a lesser extent) when travelling by coach or car.
Usually (at least in Finland) it is possible to hang your jacket in such a way that you can get the pockets face a window. Once your jacket is hanging like that, it is likely to be the best receiver position in the whole train (unless you have access to the roof...).
Trains in Japan (especially express trains) often have a window sill that a GPS can sit on quite happily, but don't leave it on the train!
Choose time of day wisely
Mapping objects when there are fewer people around may prove to be less dangerous (e.g. for features close to roads) and less stressful, and can give you the time needed to record whatever information or points of interest you seek. On the other hand, being the only person in a certain place at a certain time may equally arouse suspicion.
The night time, early morning, and public holidays lend themselves to mapping public roads and their features; for offroad features, that may be a suboptimal idea (leisure parks closed at night or certain days), so choose wisely.
As for road traffic, you will be able to go almost anywhere you wish, without being struck by other people. In some areas, you will even be able to stop anywhere without disturbing anyone, giving you enough time to take pictures or seek street signs and points of interest. Do note however that Friday and Saturday nights feature increased car accidents at these moments (and there are reasons why). Finally, if you take photos in the dark, check a few of your first shots to see if the light is enough to make your shots actually useful. I do work at early hours, and i tend to leave home half an hour earlier than usual to try new ways to go to my workplace, making new traces at once. Note however that a car driving round a housing estate slowly in the early hours of the morning could arouse suspicion from others who don't know what you are doing there.
Photographing reflective road signs at night
Attempting to use the flash from a small camera to photograph most modern steel road signs at night will produce an overexposed photograph, with the signage whited out and illegible. A convenient way to get the right amount of light from the flash is to cover it with your finger-- just enough will pass through the skin to light up the reflective parts of the sign, and the lettering will be much easier to read. An amusing, or possibly disturbing, side-effect of this technique is everything will be coloured red...
Alternatively, use some tissue or toilet paper, you will need to experiment with the layers of paper to use so that the right amount of light gets through to the sign.
Be sure not to flash other drivers for obvious reasons of road security. Consider taking non-flashed long-exposure shots instead, especially if there is ample street lighting.
Record the direction in which you took the picture
I have sometimes been wondering "Was this postbox on the left or on the right hand side of the road?". Now I record if I'm facing North or South (or whatever) when I take a picture. If using a smartphone, applications like Imageotag can record the readings of the digital compass into the Exif metadata. But a straightforward way is to add your left hand on the picture, with the index finger pointing up for North, right for East, etc.
Feel free to add to this list. Each tip should be a short paragraph.