[OpenLayers-Users] Newbie question - displaying layer of text objects on a map

[Andreas Hocevar]

Hi,

2009/3/22 Andrew Smith <laconical at gmail.com>:
> Andreas, you mentioned that if my data was in PostGIS I could use either a
> WMS or WFS to get the data.  If I went down the WMS path, I would have one
> WMS for my base map layer, and another one for my text objects layer.  My

You could also combine these into one set of image tiles. WMS has a
layers parameter. So if your wms layer params has something like

params.layers=["mybaselayer","myoverlay"];

in it, both will be rendered in one image, with the overlay not
occluding the base layer.

> understanding is that the text WMS would return a tile map of images which
> would be largely empty space with the occasional text value here and there.
> I guess this layer would be transparent so as not to occlude the underlying
> map images.

That's correct, you would have to add the transparent=true param for
the overlay.

> Meanwhile, the WFS would return the details about the text
> labels and rely on OpenLayers to actually render the vector representations.

You can also get the details of text labels using a WMS GetFeatureInfo request.

> You mentioned that WMS would be preferred if there were a 'huge number of
> features' - I'm surprised that creating all those image tiles on the server
> side is faster than adding x vector objects on the browser side (I will
> probably have a few dozen at most). Is there a certain point where it just
> makes more sense to do it on the server based on the number of objects you
> want to display?

If you expect the number of your point to grow beyond ~100, you'll
definitely be better off using WMS (especially if your users are on
Internet Explorer).

Regards,
Andreas.

-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.