What are data visualization and analyses pros/cons of QGIS over ArcGIS for Desktop?

Question

Many of my colleagues use GIS on a very sporadic basis for simple data visualization and basic analysis (clipping, buffering, etc.) and I am hoping to transition these non-core GIS people to QGIS so that we aren't relying solely on ArcGIS and it's associated licensing costs.

I've used QGIS a bit in the past, but was hoping that some of you could explain the pros/cons of using it over ArcGIS. What if someone wanted to do more advanced raster analysis? What is the support like for data formats? How about interfacing with databases?

I'm just looking for a high-level overview and any hints/tips/pitfalls you may be able to provide information on.

Answer 1

There are raster analysis tools in the latest QGIS versions: interpolation, slope, aspect, shaded relief, ruggedness, curvature, map calculator, zonal statistics, supervised classification... you name it. For even more complex things (ex: watershed analysis, image analsys, scripting, etc.) you can use all the power of GRASS without leaving the QGIS interface using the GRASS plugin. QGIS support all the formats supported out of the box by the GDAL/OGR library: soon it will be compiled against GDAL 1.9 where a few new nice drivers where added to support better proprietary formats. It can be even added the support to proprietary formats like ECW and SID. QGIS is a "natural" interface for PostGIS Databases, but it can connect also to ORACLE and ArcSDE.

Answer 2

One problem I've heard about regularly was:

"Our organization only has x Arc* licenses. Whenever I need one, they are all taken."

In such a setting QGIS will reduce waiting times, because it is always available and you can run as many copies simultaneously as you like.

QGIS also starts very quickly. Users who don't have a GIS running all the time but only start it to quickly view or edit a dataset will also find that it's faster to use QGIS.

Giovanni has already answered your questions on advanced raster analysis, file format support and databases quite well. Especially if you are planning to use the power of PostGIS, you'll find that QGIS is a very good desktop partner in such a setting.

Answer 3

QGIS is really coming on and has almost reached a point where I think I could live completely without ArcGIS (if I add a bit of scripting in GDAL/OGR plus PostGIS etc). However, ArcGIS cannot be considered to be a single package. It's more of a sliding scale as you move up through the ranks of Arcview/ArcEditor/ArcInfo. Then there are the additional extension modules. It all depends on what you can afford or what your organisation has decided to buy in comparison to what you need. So, there cannot possibly be a single answer to your question. In VERY CRUDE terms (and ignoring specialist combinations of ArcGIS extensions like Spatial Analyst, 3D Analysts, Military Analyst etc.) I'd suggest a scale something like this:

ArcView -> ArcEditor -> QGIS -> ArcInfo

But even that doesn't really give you a true comparison because, for instance, if your ArcGIS installation does not have Spatial Analyst Extension, and you want to do raster analysis, then obviously QGIS has to be the preference.

As soon as you go beyond staightforward GIS, if you throw some money at ESRI you will probably be able to make most versions of ArcGIS rival or surpass QGIS... but if you are comfortable with the FOSS world you can probably extend QGIS with a plugin, use some other FOSS solution or roll your own in C#, Python, or whatever. At this point ArcGIS wins on convenience even if not on functionality.

As for speed, ESRI claim great speed increases in v10. I've not noticed anything that's got me excited so far and I've been using v10 since it came out and have upgraded to 10.1. Empirically, I find GDAL/OGR functions written in Python faster and since QGIS is built partially on this functionality you get convenience and speed.

Lastly, if you are hiring and want "plug-and-play" GIS professionals, you'll get a better response to your job advert if your organisation uses ArcGIS than if you use QGIS.

"You pays yer money and takes yer choice" :)

Answer 4

Some random pointers to get you started:

• There is a discussion on OSGeo-Discuss mailing list:

  Can I do the same GIS tasks with OS (as with ESRI)?

• Also some pointers from Qgis-user list:

  Positive Comparison of ArcGIS vs QGIS

• Don Meltz has two blog posts on the topic as well:

  Is QGIS a viable alternative to ArcGIS?

  Round 2 in which ArcGIS throws in the towel.

  Including some benchmark results of clipping a 1.3 GB file:

ArcGIS 10, SP1

Window 7 64 bit Dell Precision m2400 laptop Intel Core 2 Duo CPU, 3.06GHz 8 GB RAM

QGIS 1.4.0

Ubuntu 11.4 Dell Inspiron 600m laptop Intel Pentium M CPU, 1.60 Ghz 1GB RAM

ARC: Over 12 hours

QGIS: 17 min 21 second

• Although a little dated and specific for libraries, this article might provide some pointers:

Francis P. Donnelly, (2010) "Evaluating open source GIS for libraries", Library Hi Tech, Vol. 28 Iss: 1, pp.131 - 151 (paper).