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Given is a map with an airport. Within a distance of 5km around the runway there is a so called no fly zone for drones (in Switzerland). I want to show this zone in a map.

What I would like to do is the following:

  1. Add a polygon around the runway (that's ok, exept that I prefer to enter the exact geo-position in decimal format instead of clicking the map).
  2. Add a second polygon that is exactly 5km from each side away
  3. Crop the corners, because these are now more than 5km away from the runway corner. To simplify one more point at 45° would be ok; I don't need a curve.

How can this be achieved with QGIS? Or better with another tool?

I have tried using buffer as suggested in the answer and this is the result:

enter image description here

Why does the buffer appear distorted instead of a uniform 5km?

Chris W
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Dominik Jenzer
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    please tell us what tool you have tried in qgis and what version you are using. edit the original question and make the change there. – Brad Nesom Mar 16 '15 at 21:27
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    Why wouldn't a Buffer work? – mkennedy Mar 16 '15 at 22:17
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    I'm curious about that as well, given that answer has been deleted. While you might have commented on that answer, you should probably edit your question to explain why a buffer won't work because it does appear to fit your requirements. – Chris W Mar 16 '15 at 22:28
  • @ChrisW I'm not sure if you can see deleted posts yet - I think that comes at 10K rep - but the answerer self-deleted - perhaps thinking that an elaborate rather than slightly expanded answer (i.e. about a paragraph rather than one-line) was being sought. – PolyGeo Mar 17 '15 at 00:53
  • @PolyGeo no, I can't, and yes, you're correct it's at 10k. If it was because it was flagged like the current one I'm not surprised. I'm seeing a number of correct if brief answers get flagged as 'low quality' and I personally think that's the wrong approach - not to mention it's contrary to the guidance which reserves that flag for answers unlikely to be salvageable via editing. Sometimes all it takes is a short, simple, clear sentence to answer the question and there's no reason for a paragraph. – Chris W Mar 17 '15 at 04:51
  • I deleted my (admittedly short) answer because I'm not particularly interested in long-windedly explaining why buffer is the answer. – phloem Mar 17 '15 at 05:09
  • @ChrisW The one line thing comes from http://meta.stackexchange.com/questions/165006/what-are-these-notices-under-my-post I am against anything but unsalvageable being flagged as very low quality too. – PolyGeo Mar 17 '15 at 05:20
  • This is a question answered by someone not very well versed in GIS concept or tools. Imho it is a good question with that starting point. – ragnvald Mar 17 '15 at 05:55

1 Answers1

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Running the buffer tool will create a second polygon offset the distance you specify from the first. Corners are radiused by default, no need to crop.

Chris W
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drvalley
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  • Thanks, buffer seams to go the right direction. I'm using QGIS 2.8.1

    What remains is, that the buffer shape is not proportional. Two oposit corners are with a real large radius, the other corners with a smaller.

    And I have to enter 0.01 as distance to have on the short side 1.2km and on the long side 1.5km from the runway to the buffer. it is not symetric... Where I'm wrong?

     – Dominik Jenzer Mar 17 '15 at 22:54
  • @DominikJenzer It's hard to say without seeing a screenshot of your data and results (which you could edit into the question). Things that come to mind include issues with the coordinate system you are using for your data (I highly suspect this given the numbers you're mentioning - sounds like a geographic rather than projected CRS), whether you've digitized the runway outline as a line or polygon, how many vertices you have, if you're using a field value for the buffer distance (because it should be the same all the way around the feature). – Chris W Mar 17 '15 at 23:50
  • @ChrisW Thanks for the hint about uploading images. I have done so far. What I have done:
    1. Add Open Stree Map Layer with OpenLayers plugin
    2. Add a shapefile layer where I added the polygon around the runways
    3. Add a buffer as you can see in the screenshot and set transparency

    Thats all I did

     – Dominik Jenzer Mar 18 '15 at 20:22
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    @DominikJenzer From your screenshot it appears you are using a coordinate system of EPSG:3857 (lower right corner). That is a geographic coordinate system known as Web Mercator or WGS84 Pseudo-Mercator and it uses degrees for units (and is not well-suited for analysis). To run your buffer you probably want to be in a projected coordinate system, such as the appropriate UTM zone for the location which would use meters for units. This QGIS documentation page should help with changing. – Chris W Mar 19 '15 at 03:54
  • @ChrisW that sound good, I will try later this day. Thanks a lot! – Dominik Jenzer Mar 19 '15 at 06:19
  • @ChrisW hmm, still some Problems. I choosed the EPSG:2056 which defines: "+proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 +x_0=2600000 +y_0=1200000 +ellps=bessel +towgs84=674.374,15.056,405.346,0,0,0,0 +units=m +no_defs" But when I enter the buffer, the image looks like the same.

    I'm looking for a CRS that shows Switzerland and works with Open Street Map. Here the link to the government website defining what to use: http://www.swisstopo.admin.ch/internet/swisstopo/de/home/topics/survey/sys/refsys/swiss_grid.html How to use this info?

     – Dominik Jenzer Mar 19 '15 at 20:46
  • @DominikJenzer To make use of that info it looks like you'd need to create a custom projection - see http://gis.stackexchange.com/questions/20566/. Also note that if your projections use different datums (ie WGS84 vs the custom Bessel based I see there), you may need to specify a transformation (note the pdf link on the right side of the page you linked to). Be sure to note where you're specifying CRSs - the data itself, the QGIS project, whether project on-the-fly is enabled - per the documentation. At this point it's sort of turning into a new question. – Chris W Mar 19 '15 at 21:40
  • Thanks @ChrisW, but I'm out. This is stuff where I have no idea what to do anymore. – Dominik Jenzer Mar 19 '15 at 22:30
  • @DominikJenzer Sorry we couldn't be of more help. It's a relatively simple operation if you're familiar with GIS, but without knowledge of the basics there's a bit of a steep learning curve to just show a buffer on a map. QGIS documentation / tutorials/ cookbook can probably get you there relatively quickly, but it does take some time/effort to learn a new subject matter and software. – Chris W Mar 19 '15 at 22:50
  • Yes, your're right. But it is not my interest to step in that deep. My job - if all is set up correctly - will be simple. And I'm sure that I will be able to do it. But to learn all that stuff just to setup my project is an overkill. Can you @ChrisW probably support with an initial project - maybe for cash? – Dominik Jenzer Mar 20 '15 at 08:40
  • @DominikJenzer GIS.SE isn't really that kind of site. Something like Elance.com or Guru.com are potential places to find contractors. – Chris W Mar 20 '15 at 19:24