Compare 2 layers and produce a map to show differences

[AlisonGregory]

I know this can be done but for the life of me I cannot remember how.

I have 2 datasets from different years.  I wish to show the difference in the areas in a third map which shows where the most change has taken place. i will then colour-code them under symbology/quantiles.

Can anyone help?

Many Thanks

Alison

[JohnSobetzer]

You might use the Symmetrical Difference tool if you have the license level for it.  ETGeowizards has a similar tool if you have the paid version of it.

If you only have the basic license you could create two new layers,  using one layer to erase overlap from the other.

I don't know if this would work in your version of ArcGIS: Compare Versions

If you don't want to create any new layers, you can use transparency on both to show areas of overlap and non-overlap.

[AlisonGregory]

Hiya John

Thanks for the advice its taken a while to get permission to download the files.  Can you advise if you have used this tool and if so do you have a copy of the Tutorial pdf? the files i downloaded do not and when I attempt to contact author it shows as a fault with the email address.

Thanks in advance

Alison

[JohnSobetzer]

If you are referring to the Compare Versions Arcscript I don't find anything on my current computers.  Sorry.  I recall using it at least once and I recall that it worked within expectations but I never used it thereafter. Most of the time I'm looking for spatial differences to correct or explain, so I simply put one layer in white over the other in red and visually errors just pop up.  Then I switch the symbology to do the same.

Another couple of alternatives you might look at.  Feature compare is one.

A simple union of the two layers works too, since in the area of overlap you will have attributes of both layers, and in areas of difference you will attributes of one or the other.  Or a simple Intersect and then use the resulting layer to block out the two input layers.