Discussion: Astigmatism & map scale

In another thread there is a lot of discussion about map scales and how to change symbol size when switching scales between 1:15,000 and 1:10,000 and other scales.

For me, suffering from terrible astigmatism, what I need in order for the maps to be more readable is more space between the symbols. So, for me personally, I prefer that the 1:15,000 symbol sizes be used on a 1:10,000 map.

But nobody else seems to like that. Is this because other people have different problems with their eyes? Or something else? Just curious

Astigmatism is not the most common problem by a long shot. Presbyopia is.

A lot of (older) people don't like the 1:15,000 symbol size just because the symbols are too small. Sorry I don't have any fancy medical terms to add to this discussion - I'm suffering from a case of acute viral nasopharyngitis and cannot think straight.

Well, I suffer from myopia, presbyopia, and astigmatism depending on the eye. Perhaps also sesquipedalia. I want larger symbols and more space. 1:7,500?

A lot of orienteers seem to have an eye missing - as well as being short-sighted and often with large blind spots.

I suffer (if that is the word) from old age and I want 1:7500 scale and 1:10000 symbols. Right now, I use magnifier goggles (2.00) AND and a hand-held magnifier when things get hairy on the map.

I'm using all of the above, and I still can't see the hairs on the map.

Sorry AZ, this is making light of a genuine enquiry. When one can see well, it's hard to understand why others are grizzling. I went to a night training last week, the map was a digital print of an ISSOM map of the city botanical gardens. I had to give up because even with a good headlamp I couldn't read the paths, let alone the rest of the detail. Sprint maps might be a special case - there is no widespread custom for a 150% enlargement for oldies, AFAIK.

So, I'm sitting in a dimly lit room right now (I am doing this intentionally, because it makes my mild astigmatism worse than normal) and browsing my old map collection. Mostly looking at old 1:15, offset printed maps.

A lot of people have commented on how a good printed 1:15 map will be sharper and easier to read than a poorly printed 1:10, and I can tell that it's true (with a magnifier) but I don't experience this as an astigmatic reader. Whether or not the edges are sharp, it all blurs together for me.

At least with the maps I'm looking at, I'm not craving more space between symbols... yes, two boulders sitting next to each-other blur together badly... but I can typically figure this out from context. (Mind you, I'm most looking at very old maps, with fairly generalized mapping styles.) However, I'm noticing that it's basically impossible for me to distinguish the fine-detail of a shape. Circular boulder symbols are basically indistinguishable from wedge-shaped boulder field symbols without a magnifier... wether or not I'm wearing glasses. Form-lines and regular contour lines look almost indistiguishable with my glasses off...

Now, I move over to a brightly-lit room, and the story is very different. This significantly improves my vision, by the 'pinhole' mechanism. I can clearly tell the boulders and boulder cluster symbols apart without magnifier now. I am now aware of 'blurriness' in the home-printed maps and the 'crispness' of the offset printed maps.

No real conclusions to add.... just a little experiment. But perhaps worth noting that for people with astigmatism (and maybe other optical aberrations), just because you can print something sharp, doesn't mean we'll see it sharp.

@blegg - interesting about the lighting. I've often thought about running with a headlamp even during the day, but decided it would take too much "explaining" so, so far have resisted. (though in a race in Waterloo one time I was so desperate I would have to run to clearings where the sun would make the map readable for me, then relocate and dive back into the forest ;-)

My astigmatism causes me to see "ghosts". So where there is one boulder shown, I will see two or three overlapping boulders (all blurry). If one boulder stands alone then I can figure out what I'm seeing, but if there are two with overlapping ghosts - then its pretty hopeless. That is why I like smaller symbol with more space between them. (this also applies to reading - without correction I can read "double spaced" text, so long as the "ghosts" from one line don't interfere with another line.

@gruver - thanks. no offence taken.

I have oblique astigmatism in my left eye, pretty much a 45 degree axis, which seemed to develop over the past 4 years or so. I have not had a problem reading maps yet. (I have glasses now that I use daily but don't wear any corrective lenses during orienteering or other sports.) My right eye is much better so I think it helps with my overall vision. I am also nearsighted, so that is probably better for the map reading than being farsighted.

Your case certainly sounds more extreme than mine, AZ. For me things just smear.

Apparently, the lighting change is really dramatic with astigmatics because our basic problem is that we have different focal lengths for various orientations. It's ok for the focal lengths to disagree a little, so long as the disagreement is smaller than the depth of focus. But in darker lighting situations, our pupils open up to bring in more light, and as any photographer knows,bigger apertures decrease the depth of focus.

When you go to an optometrist, they dilate the pupils intentionally so they can dial in your prescription under a worst-case-scenario where the depth of focus is tiny and you can sense all the aberrations.

AZ have you tried sports glasses with a brightening lens? Both Adidas and Rudy Project make them, other brands probably have them too.

I don't have astigmatism, and my ophthalmologist tells me I don't have cataracts or macular degeneration, but in dim light I just plain can't detect the presence of many point symbols drawn on a map at the 1:15,000 scale, and have a real problem with distinguishing things like .14mm contour lines when they are sitting on top of a green or yellow background. For me, having a 150% blowup of a map rather than just leaving the symbol sizes and linewidths fixed makes an immense difference. In many cases for me, it isn't a matter of being able to determine the shape of an object on the map, but a question of knowing that there is even an object there. I do use bifocal contacts which help some, but often not without coming to a stop in an open area with better lighting and staring at the map for a few seconds, and I have largely given up on magnifiers, though the shards of maybe ten or so of them previously owned by me are scattered somewhere in the terrain shown by various orienteering maps.