Category: OpenStreetMap

There’s been some discussion about the large number of small-scale mistakes present in Google Maps – there were always a few, but that number has increased dramatically recently as Google has included new sets of POIs.

What I find is that the map looks pretty good if you just need to drive around an area, but once you zoom and study it in detail, the bugs appear. Of course, if you don’t know the area, you probably aren’t going to notice the problems unless you really go looking for them, so perhaps it’s still “fit for purpose”.

My local area (pretty close to central London, not somewhere random in the countryside) has some real howlers – but then, people driving through aren’t going to notice:

Never mind, OpenStreetMap to the rescue:

For me, it’s particularly pleasing that OpenStreetMap is now becoming more accurate than Google Maps in these respects, rather than just catching up – as long as there’s a keen local contributor in each area. Adding simple (POI) data to OSM still isn’t quite as easy as it could be, although it’s much improved with recent Potlatch updates, and Mapzen looks like it could make the process easier still.

Here’s a map showing my route around the streets of Chelsea and Battersea at last night’s SLOW street-race:

My GPS didn’t acquire a good signal for the first couple of km, so I recreated my route using the following:

1. Using Bike Route Toaster I drew my course out. Important – the Data setting *must* be first set to “OSM”, to ensure you don’t inadvertently introduce copyrighted mapping data to the OSM project. You will probably also want to set the By setting to “Foot”, the map view at the top to “Street”, and toggle on/off the Auto-Routing option when you encounter paths not on the map.
2. I then downloaded it as a GPX file, using the link on the website in the Download panel.
3. I uploaded the GPX file as a trace into the OpenStreetMap project’s website (you need to be logged in to do this) and marked it as a public trace. The resulting tracklog number was noted down.
4. I went to OJW’s Static Maps website and set up the map, panning, zooming and resizing it as appropriate, entering the tracklog number, and adding a point to show the start/finish.
5. I copied the resulting image URL onto my website. As it’s just an image, no fiddling around with Javascript is needed.

One caveat is that the trackpoints only appear where you pass junctions or other nodes on the OSM mapping data – the Static Maps process doesn’t join the dots.

An easier process is to use the OSM WordPress plugin – if you have it, and WordPress, and don’t mind having a dynamic map in your post:

[osm_map lat=”51.483″ long=”-0.163″ zoom=”14″ width=”420″ height=”500″ marker=”51.49,-0.151″ gpx_file=”/files/2009/10/542876.gpx” marker_name=”camping.png” type=”OS1″]
 
(N.B. I’ve hacked the plugin to pull in map images from the new OOC OSM server of historic Ordnance Survey maps.)

[Updated] – Steve Chilton (designer-in-chief of the “standard” OpenStreetMap map) has announced the first Ordnance Survey 7th Series 1:50000 map scans are now available for tracing on to OpenStreetMap. The first ones available are in the south-west of Scotland. Further details of the project area are here.

On the right is what Girvan, a town in Ayrshire and Galloway, looks like in OpenStreetMap currently. Below that is what the 7th series imagery offers – and, bottom, the modern-day Google mapping data. This shows that, for even some sizeable towns, a 50-year-old map still has a lot to offer to enrich OpenStreetMap.

The scans have been reprojected into the “Spherical Mercator” format so they can be used in Potlatch – OpenStreetMap’s main online editor. They build on the New Popular Edition maps, which have been reprojected in England and Wales, but not Scotland so far, allowing OSM contributors to add features from the maps into the project.

Because the maps are (just) over 50 years old, their Crown Copyright has expired, which is why they can now be included in the project. Unfortunately many of the 7th series maps were printed in the early 1960s, so we’ll have to wait a few more years for these to come out of copyright and Scotland be fully covered. It would be lovely of course if the OS were to waive the copyright on these…

The maps can be seen directly here – the quality of the imagery is excellent, as can be seen in the screenshot above. Incidentally, the tilt of the grid squares is very noticeable here – the angle between grid and “true” north is quite pronounced in west Scotland.

[Update – The NPE, OS 7th Edition mentioned here, and a small number of 1:25000 OS 1st Edition maps can be directly compared on the new OOC map.]