I like to switch my HDS from the Insight maps to the Navionics card when I'm fishing a steep wall or other structure, and the Navionics card shows the depth in numbers, but not contours. Switch back to the Insight maps and my depth contours show up again.
I'm only referring to the Navionics Regions card, maybe the higher end Platinum card shows depth contours better, but I've never used any other Navionics card.
I'll also add that I'm talking about deeper water (over 70ft), not shallow water.