Ok, I have… a stupid question about maps. They are usually a representation of an area viewed from the top. But how do they work the scaling on roads that are not plane? On this representation we can see that although none of the “steets” has the same size they look equal on a top view. (I can’t sleep, sorry for the stupid question)
I’ve never seen a map that scales the width of roads based on slope.
There wouldn’t be an easy way, nor can I see anyone taking the time, to scale each road for width. The map designers pick a pen width to represent each road width. I think what you’re seeing here is an optical allusion as those don’t look like the same streets to me, and it would be impossible to determine if they were the same streets just based upon that picture. That’s why there would be contour lines or some other way to depict elevation change to show they are the same.
Most roads are close to level from side-to-side even if they have a significant slope. (Driving on a tilted road is hard.) This means that if you look at a road from the top down the width you see is very close to the actual width of the road.
There is some confusion in the OP, I think.
The link goes to a graphic showing four sets of parallel lines as viewed from the top, and then another view of those lines “in perspective”.
But maps are never drawn in perspective. A standard map is always* a “top view”, in which everything is reduced mathematically to a horizontal plane.This means that each line on the map is shown as the shortest possible distance between two points, as viewed from above, without taking into account the slope of the ground.
So a street going up a steep slope, like in SanFrancisco, will appear on the map to be much shorter than the actual length of the street if you measure it along the ground.
*exception: sometimes you’ll see a “map” drawn not as a top view but using perspective instead. But that is not really a map–it’s a diagram. A map is accurate. A diagram is not.
A map has a set scale,and you can measure any two points on the map with a ruler and accurately know the horizontal distance between them. A diagram is not intended to be an accurate map–it’s intended to be more like a photograph.
For example, lots of tourist sites pass out a diagram-like this diagram of Disney World
Consider the scale of maps.
This road atlas map appears to be 1" for 20 miles. (Estimate based on what I remember of the page size of road atlases).
We’ll pick the biggest, widest, easiest-to-depict long-haul freeway situation: 6 lanes (three in each direction), plus open-freeway median.
Minimum lane width by Interstate freeway standards is 12 feet, but we’ll round up to 15. Minimum median width is 36 feet, but we’ll round up to 40. Add four 12-foot shoulders, but round to 15.
6 x 15 = 90 (lanes)
4 x 15 = 50 (shoulders)
40 (median)
That’s 180 feet width, or .034 miles. At 1 inch per 20 miles, that scales to a line width of 0.0017 inches, or about 40 micrometers. Which is the same order of size as a human skin cell.
Accurately scaled, the largest of freeways are literally invisible without a microscope.
I think you’re also not aware that maps for places like San Francisco, are made from aerial photographs, not by someone out there measuring stuff.
Ummm…
News Flash?
Maps were being drawn of San Francisco (Yerba Buena was the Spanish name) long before airplanes were invented.
See “Land Surveying”.
Ummm…
News Flash?
It hasn’t been cost effective to make maps by surveying for decades.
Eh, not so much. The steepest street in San Francisco is 17.5°. Cosine of 17.5° is 0.9537. So the map distance is less than 5% off from actual distance.
Yup. I think the OP is talking about distance and not width.
I’ve been in GIS before it was GIS. Back in 1988 it was called AM/FM. No, not radio frequencies, Automated Mapping and Facilities Management. Back then, I worked converting paper map phone system schematics (no scale at all of course) to a digital road network that was sketchy at best. VERY high tech for its time. Everything is for its time.
Today, it totally depends on the scale and needed accuracy of the map.
Not really what you’re looking for, but I have had bike maps (in fact of San Francisco) that indicate steepness using one or more arrows, or colored lines, or some other way. It’s usually not precise, but enough for a cyclist to get an idea of what a route will be like.
That’s a good way to do it. With colors. After all, it’s steep both ways. Stuns me though how few people can read a map.
For our recreational routes. The County GIS department makes those for our trails and recreational paths. X, Y and Z. The Z coordinate (height) is exaggerated in a profile to put it on a readable map for the space given to display it on a sign.
The pro-cycle challenge is coming again next year through Summit County Colorado. We will make the route path maps. Mostly these go to EMS and such. And where aid stations and LEO’s will be. Shutting down a State Highway for a few hours is a big thing.