[OpenLayers-Users] "Lower" Overlays Not Showing When Map Is Zoomed Out

[Iain Young]

Hi All,

I have just started experimenting and playing with OpenLayers,
so this may well be a FAQ, or Newbie question, although I have
tried searching, but to no avail.

I have a scaled overall base layer, which is a PNG of the NASA
Blue Marble Image covering the entire world. I have higher res
(cropped/cut) versions for Europe, UK+Ireland, and the Southern
United Kingdom.

I've added the Europe, UK+Ireland, and Southern UK Maps as their
own "Overlay" Layers, with their correct bounds.


If I start at zoom level 0, then all 3 closer range maps are
unavailable for selection. Zooming to level 3 makes Europe
available, another zoom level, and UK+Ireland appears. Two
more zoom levels, and Southern UK shows up.

I guess I expected this, as it's related to the bounds of the
induvidual maps. However, in order to get to the appropriate
zoom level, the base layer (and "lower" layers for that matter)
end up very blocky.


How can I enable my "lower" layers to be rendered, while being
zoomed out ?

I'm guessing the answer has to do with minResolution,
maxResolution, minZoomLevel, maxZoomLevel and friends, however,
having fiddled with any and all related option, I can't seem
to change the behaviour.

Any help would be gratefully received, you can see what I mean
here: http://hal.g7iii.net/openlayers/ol-bluemarble.html


Best Regards

Iain