[Qgis-user] buffer around random points

[Milena Muehler]

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!!!!!!!