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I am trying to represent the average speed of some ship in the north of Mediterranean sea.

I am interested in aggregate the speed information by zone.

The raw data I am working with are .shp with the following information: Lat_first;Long_first;average_speed

the representation is the following: raw data

I have managed to create a vectorial grid and then calculate the average speed in every polygon as shown here and spatial join the two layers:

raw data+ grid

the result is the following picture:

average speed for zone

which has correct data but is too squared, I would like to smooth the edges to create something more similar to a heat map or interpolation.

Do anybody have dome ideas ? I am currently using QGIS but I would change if someone has a simpler procedure on some other software.

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    The short answer is that you need to increase the resolution of your grid. In this case each grid cell is the equivalent to a pixel in an image. A smoother image requires more pixels so that transitions aren't as abrupt. If your current cell/zone size is a fixed requirement, you can't get a smoother image. If you want graphics, you could convert your grid to centroid points, assign the calculated average speed as an attribute to that, then run heatmap/interpolation on those points.
    – Chris W
    Nov 18, 2014 at 19:47
  • Thanks, adding centroid to every polygon made the image much better. thank you!
    – Davide
    Nov 19, 2014 at 14:33

2 Answers 2

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I have added centroids to every polygon and this made the image a lot nicer from my point of view. thanks to Chris W

enter image description here

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  • I'm not sure why this has been downvoted. While it is a simple alteration and (at least to me) doesn't look much different than your original, the solution got you what you wanted in terms of the graphic result. My original suggestion would have gone a bit further to go more toward looking like a 'heatmap', but if you're happy with what you've got then it's enough.
    – Chris W
    Nov 19, 2014 at 19:28
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Yes, there is a tool in QGIS for creating heatmaps. It should be pre-installed (see screenshot below):

Heatmap

This link gives a detailed step by step guide on using the tool: http://www.qgistutorials.com/en/docs/creating_heatmaps.html

Also refer to:

How to adjust the granularity of a heat map in QGIS?

Creating heatmap (concentration of points) in QGIS?

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  • Thanks but I have already tried with the heatmap tool, unfortunately what I am looking for is not a concentration map or a rappresentation of points in an area, I am trying to represent the average speed value in a determined zone. I need the sum of speed in the polygon divided by the number of points in the polygon, the coloured map shows it but is too squared, I would like to create something with a better design. thanks
    – Davide
    Nov 18, 2014 at 13:25

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