Contour interval jump

[sandym]

Not sure where to put this so a new topic.

Recently we were doing some bike and hikes around the Snowy Mountains and noticed that somewhere around Round Mountain the contour interval on the topographic map switches from 10 metres to 20 metres.

This took a little mental resetting to get an image in our heads of how steep the Round Mtn FT would be to cycle. I use Memory Map so the maps are seamlessly joined which makes it a bit difficult to work out where one map ends and the next joins in.

Anyone know the history of this contour interval change?

I spent 25 years living in Canada and somewhere around the 1990's they changed all the topographic maps so everything about 2200 or 2400 metres (I can't remember which) had double the contour of the area below that elevation on the same mapsheet. It did your head in as it looked like all the valleys were outrageously steep while the mountains were flat when the opposite was true.

[north-north-west]

This struck a chord with me so I dug out my old 1:25,000 printed topos of the Australian Alps to check.
Of 35 maps covering the NSW and ACT section, 17 have 10m intervals and 18 have 20m. There's no obvious pattern to where or when the difference came in, although at a glance all the ACT sheets are 10m.
It drove me up the wall when I first realised I had to check each sheet and couldn't just assume they were consistent.

[tom_brennan]

The same is true of the northern Blue Mountains. Mt Wilson map is 10m, Wollangambe map to the north is 20m. There's a block about 4 maps wide and 8 maps high (1:25k maps) that covers largely Wollemi NP that's 20m contours.

I assume the fact that it's 4 x 8 means that it probably coincides with 4 x 100k maps (which each in turn cover 8 x 1:25k maps).

I don't know the history though. Wollemi was always hard to access, so probably had less data when they were doing the early maps.