A look at the OS OpenSpace API

OS OpenSpace Overview map
OS OpenSpace Overview map (© Crown Copyright)

This week I've spent a bit of time trying out the Ordnance Survey OpenSpace web mapping API for one of the projects I'm working on, and thought it'd be good to share some initial thoughts on it.

OpenSpace provides free access to a selection of Ordnance Survey maps for use in web projects. It was first released in 2008 as a way for non-commercial projects to use OS mapping, but has since widened its remit to allow commercial services to use the maps as well.

For a number of reasons, the OpenSpace API is different to other APIs I've worked with, and I think most of those differences are due to the fact that the API is produced by a national mapping agency rather than an international community or a corporation with international interests. In contrast to the other APIs that usually have at least some level of international mapping, you see at first glance with the OpenSpace overview map that it is focused solely on the United Kingdom.

This initial map, showing a shaded terrain view of the UK, ends just west of the border between Northern Ireland and the Republic of Ireland, leaving the west coast of Ireland off the map completely. The rest of the world is just white pixels (no dragons!). Looking at this map, I can't help but feel that filling the space surrounding the UK with a bit of sea and at least basic land outlines would help with initial impressions.

As you zoom in to the map, you get served an OS map product most suited to each zoom level, from overview maps all the way down to maps that show simplified building outlines (see the list of layers for details). Each of the map products usually shows for two or three zoom levels before switching to a more appropriate one.

As the maps have been built over the years as discreet products, each one has its own distinctive style that was designed for a particular purpose (e.g. navigating the motorway network, finding your way around cities, or walking in the countryside), and was usually designed to be used as a print product rather than on-screen. Some of the newer products and layers in the OpenSpace API have been built specifically for the digital age as maps come to be used differently than in the past.

OS OpenSpace Overview map
Overview map (© Crown Copyright)
OS MiniScale map
MiniScale (© Crown Copyright)
OS 1:250k map
1:250,000 map (© Crown Copyright)

To me, the overview layers don't feel like they have been thought out as well as you might expect from a national mapping agency, with place name labelling appearing on the second and third zoom levels in a way that doesn't look very visually appealing, along with the cut-off edges that I mentioned earlier. Zoom in beyond those layers though, and you see the nice MiniScale map which is, as described by the OS, a clear and uncluttered national map. After a couple of levels of the MiniScale map, you switch to the 1:250,000 map that's designed to show towns, major roads, railway stations, and some places of interest. In London and other cities it can be quite overpowering, but elsewhere it can give a good overview.

OS 1:50,000 map
1:50,000 map (© Crown Copyright)
OS Vectormap District map
VectorMap District (© Crown Copyright)
OS StreetView map
StreetView map (© Crown Copyright)

The 1:50,000 map was designed as a printed map for leisure use. It looks good in cities and is like a work of art in rural areas. It's the last of the print-focused map layers before switching to map products that were designed specifically for the web. VectorMap District is a background map that you can overlay your own information on without it being drowned out by bright colours and too much information. The StreetView layer isn't as subtle but also leaves enough space to visualise your own information on top of.

Overall, there's a lot of variation between each of these map products, so combining them into a zoomable map doesn't create the seamless user experience that other online maps aim to. This may be something that improves over time, but as a set of products that are available freely as part of OS OpenData they don't directly make money for the Ordnance Survey, so progress may be slow.

I'm still planning to use OS OpenSpace for the project I'm working on, but I'll likely be using only a few of the more detailed layers that are suitable for background mapping, and custom building some less detailed, lighter maps for the smaller scales.

If you want to browse the OpenSpace maps, I've put together a quick OS OpenSpace map page over on the Geobits site.