I have seemingly conflicting info in my notes concerning LCC and the following:
The scale on a Lambert conformal conic chart:
c) Varies slightly as a function of latitude and longitude
d) Is constant across the whole map
I guess both cannot be true and would appreciate some explanation. Thanks in advance for further info.
oxford blue
15th Mar 2005, 19:17
Scale on a Lambert chart is correct at the 2 standard parallels and nowhere else. It contracts within the standard parallels, being least at the parallel of origin, and expands outside them, being most at the N/S extremities of the chart.
However, scale is reasonably constant across quite a lot of Lambert charts. It depends on how many degrees of latitude there are between the 2 standard parallels. On a UK CAA half million Southern UK topo, for instance, the standard parallels are only five-and-a-third degrees apart, so the max scale error anywhere on the chart is about one-tenth of a percent. On the Jeppesen ED-6, used in the Flight Planning exam, the SPs are 28 degrees apart, so the maximum scale error is about 3% - which is why you can't use a Pooley's or Jeppesen ruler to measure distances - you get the wrong answer.
So (c) is correct. (d) is only approximately correct, and then only on some Lambert charts.
Send Clowns
17th Mar 2005, 09:30
As an extra point it should be clear that it is impossible to make a flat chart with constant scale!