[OpenLayers-Users] Positional Accuracy of Drawn Overlays

[ScottCh]

Hello OpenLayers Users,

We plan to use OpenLayers for a project that requires accurate positioning
of overlay objects drawn on an overlay layer above the map layer.  We plan
to use an updated base map layer such as one of the GSHHS tile sets.

One of the stakeholders in this project has asked me to determine how
accurate OpenLayers will be for this purpose.  In other words, if the user
draws a rectangle that precisely bounds the Isle of Wight with our product,
how far off is it likely to be in the real world?  Is the coincidence
between map layers uniform?

The first time I tried to answer this question, I responded in terms of the
map layer's accuracy.  It was pointed out to me that this is not the full
answer.  It doesn't matter how accurate the map layer is, if the points that
I have selected on my overlay layer are off in relation to the map.

I have read several postings here that relate to how OpenLayers handles map
projections, and see that it uses Proj.4 to perform its geospatial math. 
Unfortunately, I don't know enough yet to ask the right question, or where
to look in the code.  

Has anyone come across this issue already?  

I would like to verify that OpenLayers handles the intersections between the
map layer and layers above well enough for our needs, so that we can move
forward to implementation.  Kind thanks for any pointers!

Scott C.
Cary, NC USA 
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