Not sure how this is supposed to work, but here is the behavior I observe.

In Composer window:

Add map item (A). Check "Lock layers for map item".
Add map item (B). DO NOT check "Lock layers for map item".
Change symbology in main QGIS window.
Add map item (C).

A and B display old symbology. C displays new symbology. But if you make
more changes to the symbology, and want to update C, you have to hit
Refresh view button. Now, *all* map items, whether or not "Lock layers for
map item" is checked, change to new symbology. Similarly, if you change the
layer extent in A or B, they update to display the new symbology.

So it looks like if you add a map item, it will not update as long as you
leave it alone and don't hit Refresh view. But then if you're unhappy with
map item C, you have to delete it and add it in order to avoid hitting
Refresh view. Furthermore, I don't see any difference in behavior between A
and B. So what does "Lock layers for map item" actually do?

Running 1.7.4 on Ubuntu 10.04.

Thanks,
--Lee

On Mon, Mar 5, 2012 at 11:40 AM, G. Allegri <[email protected]> wrote:

> You can insert as many maps as you need and lock the layers inside the
> map.
> Set the symbology you need for one of your frames and the lock the layers.
> Then change symbology for the other, and so on...
> Look the "Lock layers for map item" inside the Map options of the left
> side frame: http://bit.ly/A8owm6
>
> giovanni
>
> 2012/3/5 Lee Hachadoorian <[email protected]>
>
>> I've used QGIS to create a layout with a main map and an inset (e.g.,
>> Continental US with Alaska and Hawai'i as inset maps at different scales).
>> But that's just two "viewports" onto the same underlying data. I wanted to
>> make a layout where the same area would be displayed with two different
>> symbolizations, side by side on the page for comparison. For those familiar
>> with ArcGIS, I would normally accomplish this with two Data Frames.
>>
>> Is there any way to do this with QGIS? Or do I have to create two QGIS
>> projects, and combine the maps externally (presentation software, page
>> layout software, etc.)?
>>
>> Thanks,
>> --Lee
>>
>> --
>> Lee Hachadoorian
>> PhD, Earth & Environmental Sciences (Geography)
>> Research Associate, CUNY Center for Urban Research
>> http://freecity.commons.gc.cuny.edu/
>>
>>
>> _______________________________________________
>> Qgis-user mailing list
>> [email protected]
>> http://lists.osgeo.org/mailman/listinfo/qgis-user
>>
>>
>


-- 
Lee Hachadoorian
PhD, Earth & Environmental Sciences (Geography)
Research Associate, CUNY Center for Urban Research
http://freecity.commons.gc.cuny.edu/
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