*squints* Could be wrong, but see "Density Search" being thrown around a lot, but feels like some are referring to Node Search as Density Search.
Now, before I completely confuse myself.. or maybe because I've completely confused myself.. Density Search is based on the ore heat map only, and it does not matter whether the ore is there or whether it spawned near the surface or not. All that matters is if the ore itself is listed in the heat map (which excludes certain special ores/rocks like "surface copper").. and if the ore is on the heat map, the best place to look for it is where there is a reading.. unless you get lucky with a deposit popping up outside the heat map area (and therefore has no propick reading)
Node Search is limited range (adjustable) and -will- detect anything in range, excluding certain special ores/rocks.
..and as with all things VS the best way to find anything is to stumble across it while your busy doing something else.. like falling down a very deep hole in the ground..