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| Subject: | [gislist] Carto Grams |
| Date: |
01/06/2006 01:55:00 AM |
| From: |
DickBoyd .. aol.com |
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Carto Grams are maps prepared using something other than distance as the
measuring stick. There are area carto grams and linear carto grams.
Perhaps you remember the red states, blue states voting maps that were
"distorted"using population or Electoral College votes for scaling. The distorted
maps more accurately depicted how close the election really was. The distorted
maps at the county level more accurately displayed the demographics of the
election.
I suggest that using only linear or area measurement to display geographic
information distorts the decision making process. Perhaps maps should be
distorted to straighten out the decision making process?
With the advent of GIS (Geographic Information Systems), depicting geographic
information with any parameter of measurement is possible. Population? Travel
speed? Elapsed trip time?
I'm trying to answer a question of why does the chicken cross the road.
Something of an origin/destination riddle. Please stick with me while I explain my
view of history of roads in the United States. If you agree with me, we can
use three models for a starting point of agreement. If we agree on these three
models and the common aspect, we can proceed to disagree. If we disagree as to
a starting point, please propose a common point of agreement.
There were three general patterns of road development in the United States.
English, French and Spanish.
English settlement in the new world was characterized by the geography of the
east coast. A few good harbors and rivers that had water falls within roughly
forty miles of the coast. Think of the Chesapeake Bay as an extension of the
Atlantic. Land transportation in English towns followed the elevation contours
established by foraging animals. The hinterlands were identified by the
waterfalls. OK, don't think Niagara size falls. Or even Great Falls on the Potomac.
Think of Little Falls on the Potomac. Towns tended to cluster at the ports.
Roads paralleled the water line, or were at ninety degrees to the water line.
Hardly an equi-angle grid. Conflicting streets crossed at what seemed to be
arbitrary angles.
French Settlements in the new world tended to be farther north on the east
coast. It was very cold in the winter. Some harbors even froze. The rivers
extended further inland before encountering falls. The ultimate being the St.
Lawrence Seaway. With portages, that seaway extends to the Mississippi River and
the Gulf of Mexico. Settlements were smaller and there were more of them. Many
failed and were never resettled, unlike English settlements. Settlements were
more seasonal than year round. Settlements were further apart in distance, but
closer together in time.
Spanish settlements were mostly in Florida north to the Georgia coast and
west to Texas and down to Mexico. The terrain was a mix of that seen by both the
English and French and the weather was more hospitable. Although the Spanish
were early settlers, wars in Europe halted western expansion. Eventually the
French took over on the Gulf of Mexico and the English took over on the east
coast.
The settlements tended to grow along the water rather than into the hills in
all three models. As settlements got larger, the roads leading to the next
town followed the body of water or went radially to the next settlement.
Settlements begin to fill in along those radials. Along the radials, flow was to the
next town. Across the radials, flow was in the town. The common factor is that
flow in one direction was "through" town. Flow at ninety degrees was "in"
town. Keeping the flows separate was a design goal.
The character of the settlements was "linear" rather than grid. Take
Alexandria, Virginia as an example. Although laid out on a grid, the town was longer
north-south than east-west. North-south expansion was limited by streams and
the need for bridges or ferries. Western expansion was limited by terrain and
eastern expansion was limited by the Potomac. Travel patterns both in length of
trip and time of day are much different for north-south than for east-west.
Alexandria uses a traffic signal control system to form platoons so a
motorist will get almost every signal green if he reacts to traffic and is traveling
in the primary direction at that time.
Please be patient, here's where the use of carto grams gets interesting. If
instead of linear measure the City of Alexandria were mapped using travel time
as the scaling factor, two maps would be required. A rush hour map and an
other time map. Think of Alexandria being mapped on a rubber sheet.
During rush hour, the major flow is north in the morning and south in the
evening. Traffic signals are adjusted to accommodate this flow. North-south
travel times are relatively short in rush hour. Off peak, the signals accommodate
east-west flow. During rush hour, Alexandria, mapped using travel time, would
appear as
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