[Qgis-user] buffer around random points

[Raymond Nijssen]

Hi Milena,

There's an algorithm "Random Points in Polygons" that will only return 
points within the polygons of a layer. So you need a vector layer for 
land for the area you are interested in.

Hope this helps,
Raymond

On 14-04-2021 08:36, Milena Muehler wrote:
> Dear community!
> 
> I’m new to QGIS and hope you can follow my process and my question. Would be more than happy to get your help!
> 
> So I have a raster layer with a cumulative value for each raster giving information about land modification (in 2016)
> 
> I have another vector layer with points providing information where an outbreak of a zoonotic infectious disease occurred (in 2016)
> 
> I want to examine the effect / association between  land modification and outbreak (I´ll do this with a binary logistic regression analysis in SPSS) therefore I want to generate a text file with values of the land modification for the location of the outbreak - I’ve done this with the tool "point sampling“.
> 
> But I also need values of land modification located at the points „no-outbreaks“. (to calculate the binary logistic regression analysis later in SPSS) Therefore I’ve generated random points. However, these points are truly random :)
> So most random point „lay in the ocean“ and therefore I don’t get values of land modification.
> 
> So my question: How do I deal with that? Can I give a kind of command that all random points have to lie on land? and to give a certain radius for the „not random“ points - outbreaks.
> 
> someone said I can do this via raster calculator. But I cannot follow it, since I don’t calculate two raster layers?! I gave me this kinda command to deal with my issue: (via raster calculator?!)
> 
> L = grid cell is on land
> 
> B = Buffer around outbreaks with radius r (tbd: minimum distance between outbreaks and random non-outbreaks)
> 
> D = L / B (difference  "L without B „ = country on which a random non-outbreak can lay)
> 
> 
> Thank you so much!!!!!!!
> 
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