joni

set terminal pngcairo font "arial,8" size 640,350
set output 'simple_distance.png'
set multiplot layout 1, 2

r(d) = d*pi/180
dist_hav(x,y,x0,y0) = 2*asin(sqrt(sin(r(y-y0)/2)**2 + cos(r(y0))*cos(r(y))*sin(r(x-x0)/2)**2))*6371
dist_sim(x,y,x0,y0) = sqrt(r(y-y0)**2 + (cos(r(y0))*r(x-x0))**2)*6371
error(x,y,x0,y0) = 100*abs(dist_hav(x,y,x0,y0)-dist_sim(x,y,x0,y0))/dist_hav(x,y,x0,y0)

set view map