[Freegis-list] time based maps

[Christian Kaiser]

Time based maps are an old concept, that's right. Sometimes, you can
find them still today. But there are a couple of problems with those
maps.
Imagine two towns A and B. They are at a distance of 10 km. But there
is a mountain between them. So you have to drive 20 km from A to B.
And you will be slower because it is a pass road. So you will have 30
minutes for the 10 km. When you like to make a time map, you have to
"flaten" the moutain. These means you have to make a sort of
projection, or a distorsion. This is possible in some cases, but not
in other cases. Normally, you will have a map which is not very
exact. So far for the problem of mapping time.
There is an algorithm who creates a sort of map from a matrix of
distances which is called "multidimensional scaling". The algorithm
is quite similar to the one for a Factor Analysis. Some statistic
programs (like SPSS) can do the multidimensional scaling and produce
simple time maps.
What actually would be more interesting is to produce isolines of
travel time that you plot upon a normal (projected) map. Perhaps
somebody knows how to do it...

Christian Kaiser




>Time based maps: the base units of measurement are *time* instead of space.
>The length of a highway line on a map represents how long it takes to drive
>from Berlin to Paris, not how many kilometers apart they are.
>
>Most of the time when people ask how far away the next town is, they don't
>really want to know how far it is, but rather how long it will take them to
>get there.
>
>I envision a set of georeferenced vectors with database attributes that
>indicated the quality of the road and the posted speed limit. When the
>cartographer creates the map she decides on a scale of 1cm:10min and selects
>the vector(s) which the map will be centered on. The software tool then
>expands/contracts the length of the vector(s) to match and surrounding
>topography is rubber-sheeted or morphed accordingly.
>
>Naturally not everybody travels the same way. Some have ferraris, others
>freightliners, still others prefer bicycles and some just like to walk. This
>just begs for an internet mapping application where the user can chose their
>method of conveyance.
>
>Also consider the application in large cities where the traffic density
>could be taken into account and near real time maps depicting how long it
>will *really* take to get to work this morning are shown.
>
>BTW, I can't take any credit for this idea, it's not mine. I've been
>thinking about for some years, ever since I saw some Inuit drawn maps from
>the 18th/19th century showing the northern coastlines of Canada. In my
>youthful arrogance I commented on how primitive the maps were, lacking all
>concept of projection or relative size. My teacher then demonstrated how the
>maps were actually incredibly accurate -- if one were paddling in a kayak
>and keeping track of how long it took to get to the next base camp. Score
>another one for "primitive" societies.
>
>cheers,
>
>
>-- Matt Wilkie
>--------------------------------------------
>Geographic Information,
>Information Management and Technology,
>Yukon Department of Environment
>--------------------------------------------
>
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