Hi Harald Vålerhaugen,
We are aware of this problem. We completely redesigned the engine of the information layer for the Q3 2010 release to increase its panning and zooming performance on large data arrays. Now it can handle up to 1000 locations (compared to 150 in previous version) or map shapes with up to 100000 total points (compared to 10000 in previous version).
However, the new engine has some side effects. Our developers have already managed to address some of them and we are currently working on the rest. The accuracy of the element location on the highest zoom levels is one of them -- it occurs because computations made to calculate position on zoom levels 19 or 20 are close to the precision provided by the double value type. The miscalculation on doubles in this case can give up to 50 centimeters difference in object location (in real world dimensions). This is 1-3 pixels on screen. The same is true for zooming and panning on highest zoom levels.
Unfortunately we cannot suggest you a workaround for this problem at the moment but we have planned several enhancements for the information layer for Q1 2011 that will solve this particular problem as well. You can track the progress of this task in our public issue tracking system here: http://www.telerik.com/support/pits.aspx#/public/silverlight/4352
the Telerik team
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