Tuesday, November 8, 2011

Google, Bing and OSM Maps: Zooming Symbolization

How Symbolisation changes with Zooming Out: A couple of weeks ago I sang the praises of Google’s 3D building symbolisation. I said putting 3D building models into Google maps with a faded gray coloring could really help people using their maps to navigate around a city. Such models represent symbolisation: the simplification of reality (3D buildings) into simpler symbols that help understanding. This week I look at how the symbolisation of buildings changes as user’s zoom out from a close in view.  I'm assuming that the user is doing some sort of navigation task again and I compare
  • Google maps
  • Bing maps
  • OpenStreetMap
Change Sucks: The first thing to point out is that evidence from my PhD student Craig’s work on the usability of maps shows that changing symbolisation as users zoom out makes it difficult for users to track what’s going on. So any sybmolisation change, say from a building polygon to a point symbol, has a mental  ‘cost’ to it, symbolisation should only change where there is good reason to do so.

Polygons to Points: So how should building symbolisation change as a user zooms out from an urban landscape? A good best practise is to have buildings represented as polygons at low altitude. As the user zooms out, the polygons become difficult to differentiate visually so it makes sense to change symbolisation to a labelled point. This is exemplified by Google’s rendering of the White house as in the screen video below. (apologies for the quality and varying sizes of the videos below, I'm experimenting with a new screen capture tool and haven't got it all worked out yet)

Points to note:
  • The symbolisation starts out as a 3D gray model
  • It switches to a polygon on zooming out
  • At all times the building is represented by a labelled point. As the user zooms out the polygon disappears and we are left with just the labelled point.
Its pretty faultless, every change in symbolisation is helping the user and it's an intuiative system.

Parliament by Google: So how does the white house example compare with the UK seat of government, the houses of parliament?

Oh dear, nowhere near as good.  A clear glitch that all labels and symbols disappear at altitude.

Parliament by Bing:  How does that compare to Parliament by Bing Maps?  Bing uses a different approach, instead of having one base map that switches symbolisation as you zoom out they have incorporated an old static style road map as the base level which changes at altitude to what amounts to a completely different map.

As you can see, the symbolisation at the lowest level is better than Google's Houses of Parliament but less good (IMHO) than Google's White House.  As you zoom out, the symbolisation stays the same which is easy to follow as a user, but the view becomes very cluttered.  The switch to a completely different map system is clumsy at best.

OpenStreetMap:  In comparison OpenStreetMap does well at low altitude with good labeling (shown here as an image rathe than a video):

Their approach is to have labels without points which then disappear at altitude while the polygons persist.  I think a labelled point at high altitude is the better system.  This alternative technique isn't too bad visually as the polygons are a neutral color and, as we've discussed,  keeping symbols the same helps users understand the map.  However, if the polygons became paled out at high altitude (so they blended in with the background) then they would work better IMHO.  This is because the road network operates as a landmark system at altitude so needs to become visually dominant over the buildings. 

Conclusion:  I wouldn't want to generalize to judging the quality of these three mapping systems on the 'Houses of Parliament' test.  As we've seen with Google, the quality can vary from place to place.  Its also easy to pick holes with mapping systems in this way, there's an enormous amount of work in producing intelligent symbolisation for multiple zoom levels across the entire globe and the visibility of polygons, labels and points at different zoom levels has to be automated in some way.  However, IMHO the symbolization could be improved in all of these three map systems and the building is important: its the seat of government in a G20 country and a major landmark in a world class city.    

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