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I am a newcomer to the world of GIS. I realized that QGIS was relatively similar to ArcGIS for Desktop.

I would like to know if the two programs are comparable in terms of computational speed.

For example, will there be differences in computation time if I made ​​a significant buffer on the same very large shapefile using QGIS and ArcGIS for Desktop?

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    Since you (as you say) are new to GIS, I'd like to make sure we have the same definition of "very large" when it comes to shapefiles. Do you mean a) a shapefile with a lot of features, b) a shapefile that covers a large extent but not necessarily contains many features, c) a shapefile with (possibly) very few features of line or polygon type but that are very detailed (contains many nodes per feature), or d) a shapefile that is many MB? Generally more nodes (!= features) requires more computing power. – Martin Aug 4 '14 at 13:57
  • I mean a perfect shapefile to have very heavy calculations =D, i don't know which is the "best" situation between a,b or c. – Staelen29 Aug 4 '14 at 14:03
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    The new threading capabilities in QGIS 2.3 + make it pretty speedy, but esri has made some improvements on their geoprocessing engine in recent years, as well (64-bit bg processing, e.g.). I think the best approach would be to benchmark a series of buffers on both software platforms. Do you have a sample dataset you can share? – MakinFlippyFloppy Aug 4 '14 at 14:50
  • Yes, let's agree on a sample dataset... – markusN Aug 4 '14 at 18:46
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    Answers are likely to be primarily opinion-based, but a couple of notable resources that may help you are: ArcGIS vs QGIS Clipping Contest Rematch, Feature comparison between QGIS and ArcGIS for Desktop, and Why is the performance speed between ArcGIS and QGIS so different?. – RyanKDalton Aug 4 '14 at 23:13
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The only way you are going to know for sure is to do it by yourself. The answer is not definitive and is dependent on your system... how many cores, what else the OS is doing at the time etc.. Yes, ArcGis and QGIS are that close that it sometimes makes little difference which one you use.

The bigger question is why buy ArcGis when QGIS is free?, the answer is the variety of tools, the API and corporate support also ArcGis is a recognized industry standard, having that on your resume is a define bonus, but then again QGIS is becoming a standard too.

Esri has been working on the low-level code for many years and many very intelligent people have optimized the nuts-and-bolts so individual processes are likely to be faster, but with that in mind the lower level code hasn't been changed much in years and it's possible that it's getting a bit antiquated.

I have bench marked QGIS against ArcGis for a capture/revision project and found that it was no slower than ArcGis and that was at version Wroclaw against ArcGis 9.3.1. Recent advances in multi-threading and 64bit (if you have a 64bit OS) coupled with the fact that QGIS will run on Linux (generally faster than Windows). ArcGis is still a single threaded application, on a CPU with less cores and higher speed ArcGis generally will perform better than QGIS and conversely with more cores and lower speed.

I am a dedicated, daily user of ArcGis but find that QGIS has its uses (frequently). I say use both and get familiar with both. They are both excellent packages and are both worth using. If you must concentrate on learning one of these packages over the other then there is a big decision to make with pros and cons for each - well worth another SE question! Personally I'd like to see an intelligent discourse on "I have the opportunity to learn ArcGis or QGIS, which one should I concentrate on?"

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