Robert,
> Whats the benefit of using OpenLayers ?
> When compared to what?
I'll try to take a stab at this question. OpenLayers has drivers for
commercial sources
like Google Maps and Virtual Earth which have their own javascript API. In
fact OpenLayers just provides
an abstraction layer on top of those APIs but uses them behind the scenes.
What does this mean - why wouldn't you just use the Virtual Earth,Google Maps,
MultiMap, or WordWind apis if you wanted to use those sources? because each
is very different and if you want to overlay your own layers from GeoServer,
MapServer, MapGuide, OpenStreetMap, or commercial layers from another OGC WMS
provider it becomes prohibitively difficult
to do so with those disparate raw apis. Not to mention writing your own raw
WMS client is not trivial. This is where OpenLayers really shines because it
allows these disparate GIS data feeds to interoperate.
So to me I think of OpenLayers as the ODBC,JDBC, DBI (except on client side of
course) of the GIS world.
There is a bit of a downside to some of this (just as there is with using any
abstraction layer). For example OpenLayers doesn't support he 3D views of
Google Maps and Virtual Earth or expose some of their other apis and there is
probably a bit (no not much overhead to wrapping this layer over). So to use
it for the other 10-15% case - you may still need to learn and get into the
guts of those apis. For the 85-90% case it works well though.
Hope that helps,
Regina
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