[Talk-GB] invisible

Henry Gomersall heng at cantab.net
Tue Jan 18 13:32:28 GMT 2011

On Tue, 2011-01-18 at 13:00 +0000, Graham Jones wrote:
> I think you are describing what my examples do - for example the map
> at http://maps.webhop.net/topo uses a simple base map and the
> OpenLayers javascript program running in the web browser draws the
> selectable overlays on top of it - the overlays are PNG images with a
> transparent background.   Or maybe you meant some sort of clever
> bitmap with layers defined within it?   Whether it is efficient or not
> depends on what you are trying to do with the overlays - for single
> points (e.g. the power stations themselves on my map) holding bitmaps
> is much less efficient than storing the locations of each power
> station - you could have OpenLayers take the locations of the points
> and plot them. 

What you describe is exactly what I meant.

Regarding the bitmaps being less efficient, do you have any evidence for
this? I mean, naturally there is going to be a trade off between
computation and storage, but compression of things like power station
points is going to be pretty efficient.

It might be that a good compromise would be rasterised layers that use
only a single colour per layer (which can be stored incredibly
efficiently) with a client-side beautification and overlay step. It
would also be very simple then to change the colours of features.



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