level of detail – scale matters

We get used to being able to zoom into every document picture and map, but part of the cartographer’s skill is putting the right information at the right level of detail.  If you took area maps and then scaled them down, they would not make a good road atlas, the main motorways would hardly be visible, and the rest would look like a spider had walked all over it.  Similarly if you zoom into a road atlas you would discover the narrow blue line of each motorway is in fact half a mile wide on the ground.

Nowadays we all use online maps that try to do this automatically.  Sometimes this works … and sometimes it doesn’t.

Here are three successive views of Google maps focused on Bournemouth on the south coast of England.

On the first view we see Bournemouth clearly marked, and on the next, zooming in a little Poole, Christchurch and some smaller places also appear.  So far, so good, as we zoom in more local names are shown as well as the larger place.

bournemouth-1  bournemouth-2

However, zoom in one more level and something weird happens, Bournemouth disappears.  Poole and Christchurch are there, but no  Bournemouth.


However, looking at the same level scale on another browser, Bournemouth is there still:


The difference between the two is the Hotel Miramar.  On the first browser I am logged into Google mail, and so Google ‘knows’ I am booked to stay in the Hotel Miramar (presumably by scanning my email), and decides to display this also.   The labels for Bournemouth and the hotel label overlap, so Google simply omitted the Bournemouth one as less important than the hotel I am due to stay in.

A human map maker would undoubtedly have simply shifted the name ‘Bournemouth’ up a bit, knowing that it refers to the whole town.  In principle, Google maps could do the same, but typically geocoding (e.g. Geonames) simply gives a point for each location rather than an area, so it is not easy for the software to make adjustments … except Google clearly knows it is ‘big’ as it is displayed on the first, zoomed out, view; so maybe it could have done better.

This problem of overlapping legends will be familiar to anyone involved in visualisation whether map based or more abstract.


The image above is the original Cone Tree hierarchy browser developed by Xerox PARC in the early 1990s1.  This was the early days of interactive 3D visualisation, and the Cone Tree exploited many of the advantages such as a larger effective ‘space’ to place objects, and shadows giving both depth perception, but also a level of overview.  However, there was no room for text labels without them all running over each other.

Enter the Cam Tree:


The Cam Tree is identical to the cone tree, except because it is on its side it is easier to place labels without them overlapping 🙂

Of course, with the Cam Tree the regularity of the layout makes it easy to have a single solution.  The problem with maps is that labels can appear anywhere.

This is an image of a particularly cluttered part of the Frasan mobile heritage app developed for the An Iodhlann archive on Tiree.  Multiple labels overlap making them unreadable.  I should note that the large number of names only appear when the map is zoomed in, but when they do appear, there are clearly too many.


It is far from clear how to deal with this best.  The Google solution was simply to not show some things, but as we’ve seen that can be confusing.

Another option would be to make the level of detail that appears depend not just on the zoom, but also the local density.  In the Frasan map the locations of artefacts are not shown when zoomed out and only appear when zoomed in; it would be possible for them to appear, at first, only in the less cluttered areas, and appear in more busy areas only when the map is zoomed in sufficiently for them to space out.   This would trade clutter for inconsistency, but might be worthwhile.  The bigger problem would be knowing whether there were more things to see.

Another solution is to group things in busy areas.  The two maps below are from house listing sites.  The first is Rightmove which uses a Google map in its map view.  Note how the house icons all overlap one another.  Of course, the nature of houses means that if you zoom in sufficiently they start to separate, but the initial view is very cluttered.  The second is daft.ie; note how some houses are shown individually, but when they get too close they are grouped together and just the number of houses in the group shown.

rightmove-houses  daft-ie-house-site

A few years ago, Geoff Ellis and I reviewed a number of clutter reduction techniques2, each with advantages and disadvantages, there is no single ‘best’ answer. The daft.ie grouping solution is for icons, which are fixed size and small, the text label layout problem is far harder!

Maybe someday these automatic tools will be able to cope with the full variety of layout problems that arise, but for the time being this is one area where human cartographers still know best.

  1. Robertson, G. G. ; Mackinlay, J. D. ; Card, S. K. Cone Trees: animated 3D visualizations of hierarchical informationProceedings of the ACM Conference on Human Factors in Computing Systems (CHI ’91); 1991 April 27 – May 2; New Orleans; LA. NY: ACM; 1991; 189-194.[back]
  2. Geoffrey Ellis and Alan Dix. 2007. A Taxonomy of Clutter Reduction for Information VisualisationIEEE Transactions on Visualization and Computer Graphics 13, 6 (November 2007), 1216-1223. DOI=10.1109/TVCG.2007.70535[back]

First version of Tiree Mobile Archive app goes live at Wave Classic

The first release version of the Tiree Mobile Archive app (see “Tiree Going Mobile“) is seeing real use this coming week at the Tiree Wave Classic. As well as historical information, and parts customised for the wind-surfers, it already embodies some interesting design features including the use of a local map  There’s a lot of work to do before the full launch next March, but it is an important step.

The mini-site for this Wave Classic version has a simulator, so you can see what it is like online, or download to your mobile … although GPS tracking only works when you are on Tiree 😉

Currently it still has only a small proportion of the archive material from An Iodhlann so still to come are some of the issues of volume that will surely emerge as more of the data comes into the app.

Of course those coming for the Wave Classic will be more interested in the sea than local history, so we have deliberately included features relevant to them, Twitter and news feeds from the Wave Classic site and also pertinent tourist info (beaches, campsites and places to eat … and drink!).  This will still be true for the final version of the app when it is released in the sprint — visitors come for a variety of reasons, so we need to offer a broad experience, without overlapping too much with a more tourism focused app that is due to be created for the island in another project.

One crucial feature of the app is the use of local maps.  The booklet for the wave classic (below left) uses the Discover Tiree tourist map, designed by Colin Woodcock and used on the island community website and various island information leaflets.  The online map (below right) uses the same base layer.  The map deliberately uses this rather than the OS or Google maps (although final version will swop to OS for most detailed views) as this wll be familiar as they move between paper leaflets and the interactive map.


In “from place to PLACE“, a collection developed as part of Common Ground‘s ‘Parish Maps‘ project in the 1990s, Barbara Bender writes about the way:

“Post-Renaissance maps cover the surface of the world with an homogeneous Cartesian grip”

Local maps have their own logic not driven by satellite imagery, or military cartography1; they emphasise certain features, de-emphasise others, and are driven spatially less by the compass and ruler and more by the way things feel ‘on the ground’.  These issues of space and mapping have been an interest for many years2, so both here and in my walk around Wales next year I will be aiming to ‘reclaim the local map within technological space’.

In fact, the Discover Tiree map, while stylised and deliberately not including roads that are not suitable for tourists, is very close to a ‘standard map’ in shape, albeit at a slightly different angle to OS maps as it is oriented3 to true North whereas OS maps are oriented to ‘Grid North’ (the problems of representing a round earth on flat sheets!).  In the future I’d like us to be able to deal with more interpretative maps, such as the mural map found on the outside of MacLeod’s shop. Or even the map of Cardigan knitted onto a Cardigan knitted as part of the 900 year anniversary of the town.


Technically this is put together as an HTML5 site to be cross-platform,, but … well let’s say some tweaks needed4.  Later on we’ll look to wrapping this in PhoneGap or one of the other HTML5-to-native frameworks, but for the time being once you have bookmarked to the home page on iOS looks pretty much like an app – on Android a little less so, but still easy access … and crucially works off-line — Tiree not known for high availability of mobile signal!

  1. The ‘ordnance‘ in ‘Ordnance Survey‘ was originally about things that go bang![back]
  2. For example, see “Welsh Mathematician walks in Cyberspace” and  “Paths and Patches – patterns of geognosy and gnosis”.[back]
  3. A lovely word, originally means to face East as early Mappa Mundi were all arranged with the East at the top.[back]
  4. There’s a story, going cross browser on mobile platform reminds me so much of desktop web design 10 years ago, on the whole iOS Safari behave pretty much like desktop ones, but Android is a law unto itself!.[back]