I went back to Latin word site, and first thing I saw was "raster" defined as "hoe".
So what is one important thing a gardener can do with a hoe? Make parallel grooves on his plot for planting small seeds in rows. Into my mind popped "raster" on a TV monitor
the horizontal parallel lines you used to see before the set was tuned in.
5Ger, screen < ML rastrum, rake < L, hoe, mattock < rasus: see RAZE6 the pattern of illuminated horizontal scanning lines formed on a picture tube when no signal is being received