I've seen a few comments about the contour interval being the problem, but I don't really think that's the main issue. There shouldn't be *that* much information lost just because of the difference between 5m and 20ft. I think the problem is that these are bad 20ft contours and there hasn't been much attempt to make them better. A lot of the drainages missing from the map should absolutely be wiggles in the 20ft contours, but there's just nothing. It can make for a pretty frustrating experience even if you know what to expect.