[Qgis-user] Making Maps of differences between two maps

[Carlos Cerdán]

Hi Peter:

Suggestion one: I think it's better to make the work just in one layer, so
you can style it for each year... then you need suggestion two

Suggestion two: To add features:
1. Make editable the target layer.
2. Select and copy the object from another layer that you want add to
target layer
3. Paste. It's supposed that these two layers are same class: point, line
or polygon

Good luck

Carlos


2013/12/12 <HPETER784 at aol.com>

>  Version 2.0 on Windows, just loaded normally.
> Here is my problems.
> I am studying the growth of a village in Somerset over the past few
> centuries.
>
> I have an esri file of the roads in 2006.  I have a paper map of the roads
> in 1969. First, I make up an layer for the roads in 1969 by deleting
> features from the 2006 layer and saving the result in the 1969 roads
> layerTo get a difference map, that is (say) the 1969 roads in black and the
> new (1969 to 2006) roads in red, I map the 2006 map in red, then overlay
> the 1969 in black.  But the 'black' is not black, but some combination of
> red and black.  I have tried the options in Layer blending mode (page
> 73-74) without success.  Question One is  - how do I overlay one colour
> over another and still retain that colour?
>
> Another way I tried was this.  From the attribute table for 2006 road map,
> I selected those features corresponding to the new roads (page 105-106 in
> the User Guide) and saved them as a new layer , the difference layer.  Then
> just mapped the 1969 map and this new layer.  This worked.  Unfortunately,
> I missed a few of the new roads, so I want to select more features from the
> 2006 layer and add these to the already existing difference layer.  I
> cannot find out how to do this, that is add features to an already existing
> layer.  Question Two is; how can one add features to an already existing
> attribute table?
>
>  I suppose all this is quite simple, but I am a beginner.
>
> Peter,
> 15 Woodbarton,
> MILVERTON,
> Taunton TA4 1LU
> 01823 400 272
> hpeter784 at aol.com
>
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