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I have been working with GIS and remote sensing in an university and professional environment some ten years ago (ArcInfo etc), so I have some experience even though somewhat outdated

Right now I am looking for an GIS application for a small farming project and I found GRASS and QGIS projects which sound both very interesting. However I do not really get the difference between the two programmes. Which one do I use best for simple thematic maps with different layers?

Thank you very much in advance.

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2 Answers 2

They have a major difference on how they deal with vectors and this is very important:

GRASS has full/real topology support, that means that a single boundary can share several areas .

QGIS is primarily non-topological or "spaghetti" , adjacent area boundaries are duplicated.

And they relate in the way that Qgis can display and edit GRASS vectors through the GRASS plugin, preserving the topology.

So since you plan to work with thematic maps, which I assume are in vector format, I would recommend also take a look at this article who points some info on topology.

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is this answer still valid? I believe QGIS has topology now. docs.qgis.org/2.2/en/docs/training_manual/create_vector_data/… –  tkurk Sep 10 at 22:45
    
Yes, it's still valid. The link points to a discussion of using the editor in a manner that preserves topology, but it is doing so by changing nodes/arcs between adjacent polygons in the same way. The polygons are still stored completely independently, which means nodes/arcs are duplicated. In a truly topological vector data format, like GRASS uses, the nodes/arcs are stored once and shared between the adjacent polygons. –  Lee Hachadoorian Sep 11 at 2:53

GRASS is usually used for scientific purposes. So unless you want to do some sophisticated spatial analysis or routine, just stick with QGIS. Also GRASS works with its own formats so you will have to import/export data to exchange data with someone. Even if you will need sophisticated spatial analysis or routine at some point you will be able to do it with SEXTANTE plugin (GRASS support included) for QGIS. In QGIS there was also a plugin for communication with GRASS but SEXTANTE took its place. I think for simple mapping purposes you should use QGIS.

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SEXTANTE is an interface to GRASS hence why the GRASS plugin is dead. –  Nathan W May 6 '13 at 8:57
    
Dead or unmaintained? –  maning May 6 '13 at 9:39
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Unmaintained. It should still work in 1.8 but in 2.0 it is better to use SEXTANTE. –  Nathan W May 6 '13 at 10:02
    
Thank you very much for the answer. I'll give it try and will probably be back in the forum at some stage. –  Alex May 6 '13 at 10:46
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Enjoy grasswiki.osgeo.org/wiki/GRASS_and_QGIS and grasswiki.osgeo.org/wiki/GRASS_and_Sextante (the latter has the advantage that the QGIS user can run GRASS GIS commands right away while the first solution is more complicated to use. BTW: GRASS GIS is generic and not only for scientific purpose. But many algorithms have a scientific origin... brought to the masses :) –  markusN May 6 '13 at 14:10

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