Discussion: ISOM to ISSOM conversions

Let's say the terrain didn't change at all. How useful can the ISOM map be, or is remapping from scratch usually the way to go?

I've done sprint maps where there was an existing large scale ISOM map of the area. While it can be useful for object positions, and vegetation, there just isn't enough information encoded about the passibility of features to make a good ISSOM map without fieldwork.
I would use the existing map as a template and redraft it as an ISSOM map. Then use that as a base for your fieldwork and assume you will have to do a lot of reclassification and addition of detail.

If I was Simmo, I'd agree with the above comment.

I wouldn't bother, to be honest - start from scratch. If you have no other base data to use then use the ISOM for that, but don't just change the scale of the OCAD file and edit it. I tried to use a 1:10000 map as the basis for a (forest) sprint map, and gave up after the first fieldworking session.

* Symbol size (once you blow it up 2.5 times to change the scale) introduces too much positional error.
* The amount of detail you have to generalise at 10000 is totally different to what you can/should draw at 4000.
* Symbols in urban areas are too different - canopies, roads-as-a-single-line vs drawing each edge independently, the lack of boulder field symbol in ISSOM, etc etc etc.

If I was Juffy, I'd agree with the above comment.

I agree with Juffy - start from scratch. I did try to partially convert a ISOM map to ISSOM - I say partially because I made no attempt to convert the 5m contour interval to 2m or 2.5m. I added a few form-lines - drawn by eye where pretty obvious. I'd say the map is just usable (eh, tRicky?), but not for anything higher than a local event.

If I was tRicky, I'd agree that the map is just usable.

Thanks all... confirmed my suspicions.

I would add a qualifier... forest sprint area... it would depend on the case. Built-up areas... start from scratch.

You know my experience with Berkeley campus... old ISOM maps were mapped with a lower degree of accuracy. Just trying to update the old map, I spent too much time trying to figure out distortions. It was easier to start from scratch.

The only places I can assume you'd be considering this (Stanford or Indian Valley?), I think you'd have a similar experience. I think Indian Valleys forested areas would be extremely difficult to map at sprint standards though... and probably not worth the effort.

I do find the old editions very useful to have on-hand when drafting though. A really nice resource to help you think about how to generalize, and make sure you didn't miss anything important.

IL the area I did was forest, with a lot of granite, which needed to be completely re-interpreted. Had 2.5m contours been available, all the contours would have needed considerable tweaking. Granted the original ISOM map wasn't very good, but for any forest area with a lot of detail, I wouldn't recommend trying to convert to ISSOM unless the original ISOM map was produced from lidar (with the original file with extra contours still available to import) and was made by a top mapper.

I once thought close to home maps were easy. We did all our urban parks at 1:5000 using the ISOM 1:10,000 symbol set. And gradually synchronised the symbol sets and joined them all together (we live in a long river valley, the banks are all "park").

Can't avoid any longer converting them to ISSOM. It takes forever. Not so much the fieldwork, but the drawing. Edges everywhere. Porches and alcoves. And the slightest departure from 90 degrees for a building stands out like a sore thumb.

Not so much the fieldwork, but the drawing.

This.

My rule of thumb for forest mapping is 2 hours fieldwork = 1 hour drawing. Sprint is more like 1:3. Drawing sprint maps properly is hard.

Yes it is. That's why I leave sprint mapping to the experts.