View topic - Topo maps are unreliable when away from the travel routes

I should clarify my comments. I do not a consider unmarked rapids a topographic map flaw - these maps can't always provide this detail. Cultural data should always be approached with skepticism (like portages). Roads get quickly overgrown, new roads quickly appear. Many maps get updated without new field checking. A mis-marked portage, should never lead to a death - just a bad portage.

Not to worry, paddleN, your observations are just as valid as mine. We just have different areas on our mind.

My point is that the maps are interpretations of the nature rather than geometrically true representations. In different areas, this will work out differently, and in some complex areas like this Kawartha back country, it can be quite a surprise. Beyond that, I believe that the people that draw maps to take more license in areas where they expect fewer people to travel - but I easily concede that is mere speculation.

I am having trouble uploading images to the Gallery, but I have managed to get two examples of that specific area up-loaded.




Here's the map (basemap) with the arrows' tips pointing at the specific location where the images were taken.



Point 1:
Taken facing NE


It looks good on the detailed maps, but on the 1:50,000 I naively expected a creek. Swamps are nearby, of course....







Point 4:



Taken facing SW



The 1:50,000 topo shows it as a creek, the base map allocates a lot more water surface.

About the Missinaibi portage:

I remember Hap's article in the Globe and Mail when he raised it to the level of National attention: basically a mapping error and the officialdom's sluggish response(to the point of just covering the a$$ but damn the consequences!). He was livid and probably still is sore.

No, I did not mean to talk about errors - I always expect them when people are involved. In that Missinaibi case, the paddlers had relied on the map for the correct location of the portage and thus passed the point of no-return, with fatal consequences.

Sorry for sidetracking the thread, but ...
Was there indeed a mapping error?
The evidence available at the moment to me says no.
A vital piece of evidence is missing though, namely whether the cart trail extends above the falls.
One might conjecture that it does. Would it not be pointless to cut the trail below the falls only? It would be like building a bridge halfway across a river.
Yours in paddling, Allan

_________________

If it's not worth doing to excess, it's not worth doing at all. (AJ)

Erhard, sometimes it's worth checking air photos for more accuracy in ground detail, if an area's going to be explored more than just passing through on a canoe route.

In the past, after spending time poring over top maps, planning out what surface features I was going to check out, sometimes I'd look at the air photos for more information... the difference in the appearance in the air photo could be striking after becoming familiar with the features on the top map. The air photo at times gave a much different impression of what was actually there.

Margins of lakes, and wetlands area and occurrence seemed to vary the most from what was printed on the top map. At times there was wetlands vegetation indicated on the air photo when there were no wetlands at all on the top map.

Viewing the photos through stereo viewers for a 3-D picture was the best way to get some feel for the character of the landscape, and I'd write the details down on the top maps for when I was bushwhacking through.

Air photos and stereo viewers used to be available at Queen's Park for free viewing during their office hours, unfortunately this service was eliminated because of budget cutbacks. Now the photos are sold online and using them costs more.

The satellite photos on Google, even if they are the darker, high-resolution variety, still don't seem to provide as good an idea of the landscape features as the 3-D air photos did.

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I guess my point was not to read more into a map than what is available, then call the map incorrect, or a poor representation. That creek line is probably around 5-10m wide - so how can you represent a little pond? A line with a swamp is a perfectly good representation of that photo given the limitations of a 1:50,000 map.

I'm not familiar enough with the Ontario Atlas. In general, I don't trust any map that is not produced by the US or Canadian Survey.

-Andy

Good point. I used to stop by that Queens Park office once in a while, but now I try to do everything from the computer.

Actually, when we decided to putter around that area, we were quite willing to be surprised - that's part of the adventure. Once I can upload images to the Gallery again, I'll show two more examples where we got "surprised"...

That was an example where the base map allocates too much water surface, an observation that was put forward by D Burgess:

In that example I agree with you: topo represents nature better.







Interesting point. The Ontario maps are probably based on federal data, at least the water layer of the maps. I know that Ont. has been struggling to get a single map data base for years now, and they'd be mad to use anything but the Canadian Survey data for that layer.

About the Thunderhouse Falls Missinaibi portage:

There is actually an old portage trail on the right side of the river. I personally walked on it (just as a hike; we portaged on current official left side portage). I know the person who in late 50ies or early 60ies worked on it (trail maintenance?).

I didn't see the topo map to know how/where exactly was the start of portage marked there.

I have several older 1:50's which still show portage trails. I believe the practice of showing these on topo's stopped quite a while ago. Portages are often dynamic and fleeting in geographical timelines. I know of several cases along rivers when I have decided that a portage on one side is no longer viable, due to wash outs, shifting log jams or a variety of other natural occurences. I'll then cut a new one on the other side if able to do so. I have seen so many portages disappear due to natural causes, such as blowdowns or fires, or human impacts, such as logging, that keeping an accurate track of their locations becomes more a matter of approximation than exact science.

On the other hand, I have been extensively using my GPS along with my standard 1:50 topo's for the past few years, and I have yet to find a major discrepancy on either, or between either. However, as all sensible canoeists know, information related to ports, campsites, rapids, etc can be trusted as much as you trust and know the person you get the info from. I would suggest that following outdated portage info on a 1:50 would be problematic. A port that is located on a map that is contrary to one's knowledge of the area doesn't mean that it is a mapping mistake. It just might mean that there might have been a port there when the map was made, and that the information is now out of date. If one thinks that the Canadian 1:50 topo maps are up-to-date for human impact features such as roads, then disappointment will be the order of the day. many of the older logging roads, etc shown on the 1:50's and even the provincial maps are no longer passable, and many have completely gone to seed. I have to up-date my local maps on a yearly basis from the logging companies, as new roads appear, and old ones become decommissioned or fall into a state of permanent disrepair.

I believe the older maps were made manually from aerial photos using stereoscopes to bring out the contours.
Survey control points had to be placed at regular intervals....Remember the White crosses seen along roadsides and power lines. So two factors are at work, someone had to interpret 1950's or 1960's aerial photos .. which only showed conditions, wet or dry, on the day the plane flew over. And remote spots probably had fewer control points to check into so the accuracy might be lower too. The scale between control points might be a bit variable as the area would be proportioned to fit. An area seen in a winter photo, with a bit of snow on the ground, could easily look entirely differently during spring high water.

Hope this helps

Douglas

The process was called photogrammetry (sp?).
An aircraft flew over the area and took photos with cameras on the wings.
As Douglas said, then some poor sod matched up the photos, looked at one through one eye and at the other with the other and drew features and contour lines by hand.
That was how things were done until sometime in the 60s, I think.
It's amazing that so few errors were made. The only one I know of is on the French somewhere around Devil's Chute.

On the Thunder House Falls item:
So the cart track does indeed start far enough above the falls on river right?
So unless the river was in flood or near it, those guys just missed it?
So neither government has any responsibility, moral/legal/whatever for those deaths?

Yours in paddling, Allan

_________________

If it's not worth doing to excess, it's not worth doing at all. (AJ)

If someone knows better, correct me:

* there's a cart trail on the river right - I don't see it on any of the maps, and it probably is not the traditional portage. The reason may be that coming up right after there is a long stretch of rapids (Stone R and Long R) following with portages on the right, and when a "cart trail" was put in place, it was expedient to start the whole thing above Thunderhouse.

* the original portage for Thunderhouse is on river left, with a number of different landings. Here's how Hap's book (1994) describes the issue:


* the map 42 j/3 I have is dated 1977 with interim corrections 1996. It shows the portage on river left.

My 42J/3 map is marked
.... COPYRIGHTS RESERVED 1977.
Interim corrections 1978

The following coordinates are UTMs, NAD27, plus/minus 50 m.
On my map, a dashed line starts on river right about 800 m above the small stream on river right (the one that joins Coal River), just at the start of the first marked rapids, and maybe 200 m above the start of the portage on river left.
The coordinates of the starting point are 439/453.

The dashed line splits at the falls.
One dashed line runs straight toward the bay near 418/519;
the other, marked POR, returns to the river near 428/474, below the falls.

I'll try to scan my map and post it; it is heavily annotated in that region though.

I don't know how far up the river-right side Wolverine got

Regards, Allan

_________________

If it's not worth doing to excess, it's not worth doing at all. (AJ)

posting Allan's Map