# How is the terrain displayed on the ND in a A320?

When you turn on "TERR ON ND" in a A320, you see terrain info on you navigation display (ND), but where does its source come from ?

• if data comes from FMGS stored inside its memory, then how come it cannot display it in all bounds of the display (see picture) ?

• if data comes from the nose radar, then how is it possible to see oceans when you're on the ground in an airport, say in JFK for example ? The radar beam would never be able to get to the water directly.
• how come it cannot display it in all bounds of the display (see picture) ? uh? I've seen the picture, but I don't get what you mean with "all bounds of the display" – Federico Sep 12 '16 at 8:55
• I mean like below the aircraft for example (and on the sides) – Matt Sep 12 '16 at 9:11
• aircraft are non-holonomic systems, they can't move sideways and they can't pull back mid-air, so way waste precious screen real-estate for stuff that does not influence you? – Federico Sep 12 '16 at 9:16
• an A320 is not a fighter, its manoeuvrability is limited. you can be sure that they evaluated this when deciding exactly which angle to display – Federico Sep 12 '16 at 9:22
• Regarding the area displayed: The full 180° are only covered by the recent versions of the EGPWS. the reason is likely that calculating relative altitudes is a heavy workload for the EGPWS CPU, and with new chips, more pixels can be computed in a decent time. See how slowly the display is refreshed in this video. – mins Sep 12 '16 at 11:21