Why metric topography tends to suck

[jrad]

I was planning a route and just this morning realized that a critical section was in an area covered by metric topographics albeit converted to English intervals by Caltopo. The problem is the conversion by Caltopo resulted in my route suddenly going from 80-foot contour intervals (easy!) to the MUCH more informative 40-foot contour intervals (pretty steep!).

What a difference that makes!

I have spent over 50 years interpreting topo maps based on the English system using 40-foot intervals or even 20-foot intervals. I can tell at a glance when a slope is too steep or may be a serious problem with that fine grain definition but NOT at 80-foot intervals.

Caltopo offers conversion of everything to 40-foot intervals or even less. The problem is that the conversion takes a long time (on my computer, which is damn fast, I'd say) AND looks very sloppy and confusing. For some reason they do not clean up the result but leave a ton of extraneous messy lines to wade through.

BEFORE conversion (40-foot intervals default from English standard + clean conversion of metric but to 80-ft intervals):
I know for a fact that these (upper half) topo maps were converted from metric topos because before Caltopo got involved, they were ONLY metric (very jolting transition).

topo example.png (101.43 KiB) Viewed 169 times

AFTER conversion (40-ft lines selected, English AND metric both converted to 40-ft intervals):

example topo converted 2.png (104.72 KiB) Viewed 169 times

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NOTE: I am 100% in favor of the metric system for ALL science and many other uses, But the metric system is inherently NON-human-body oriented. It needs at least one more distinction such as 1/3rd meter that one might call a "tertian" or some such ... something corresponding to a human feature such as a foot - one might call it a "bigfoot" measure. Or something. At any rate I abhor unadulterated metric topography. It really sucks, even when converted to English, as long as the intervals are too broad. There is simply too little information (way less than half, I'd say!). The old English 40-foot contours hit a real sweet spot in intuitive comprehension. Metric is anything BUT intuitive. Anyway, that's my 2 cents or 4 ha'penny's worth.

[Wandering Daisy]

I suppose those who grow up in the metric system and have historically used metric maps, would say English Unit maps suck.

The metric contour interval is about 66 feet elevation, or 26 feet more than the 40-foot interval and 14 feet less than the 80-foot interval. The map that shows Kennedy Lake in Emigrant has an 80-foot interval more similar to a metric map. You would get a similar steepness disconnect with that map. I think we all internalize contours with enough use.

Regardless of which units or intervals you internalize, contour maps are simply gross representation of the steepness which can be very uneven. The contour lines themselves say nothing of the nature of the slope -uniform or stairsteps. I find that the modern maps are smoothed too much and sacrifice the character of the landscape, regardless of being metric or English.

It is not the units used. Computer drawn maps from DEM data generally are too smooth- make things look very "civilized" so to speak. I love the older maps with all their wiggly, sharp, ugly lines!

[Gogd]

I concur with WD.

I'd further add neither metric or imperial U/M contours of topo maps offer enough detail to make the difference significant. More important is the scale of the map. If you know the scale and the interval between topographical contour lines, you can calibrate your mind's eye to comprehend the lay of the land. If I had a gripe, it is a bench formation 15' high can stymie a XC route - as is frequently the case - yet it will not show up on any topo map, regardless of contour scale or U/M. (wha wha, right!?).

Ed

[Teresa Gergen]

Lidar point cloud data (not DEMs) is being used on the listsofjohn.com website to hand-analyze more accurate elevations for peak summits and saddles. Much of CO has been analyzed and some small dent has been made in other states, moreso in the west. The High Sierra has very little lidar data available yet, but analysis will be done as quickly as possible when it is. The frequency of errors with topo contours, spot elevations, BM elevations, etc is absolutely astounding, regardless of if the maps are imperial or metric.

Example: Mount Maclure is a 13er, not a 12er:
https://listsofjohn.com/peak/32443

This has had a very significant impact in the peak-bagger world for elevation-oriented peak lists, not just due to elevation changes, but also because a peak's prominence is used to determine if a peak is ranked (300 ft on LOJ) or not, and thus on a list. It's also affected county highpointing and even state highpointing.

https://listsofjohn.com/peak/218278

On that last example, the contour isn't even drawn in the correct location.

[thegib]

I've no allegiance to the crown but I find 66.5' inferior to 40'. In this I wish we'd revert back.

[Love the Sierra]

Thank you all! For a no vice navigator, all good info on which maps to buy and to pay attention to what I see on CalTopo. Perhaps taht has been the reason for many of my navigational snafus in the past couple of trips? Yes Ed, 15’ is a big deal and I have learned the hard way, it doesn’t show on the map!