Jump to content

 
Photo

Best Projection for True Measuring

- - - - -

  • Please log in to reply
2 replies to this topic

#1
dirtyjeep

dirtyjeep

    Newbie

  • New Member
  • Pip
  • 1 posts
  • Location:San Francisco Bay Area
  • United States

Hello All,
I'm working on a map/chart printout of points and lines with a latitude and longitude overlay and need my customers to be able to use the scale bar (in nautical miles) and longitude line to measure nautical miles. My first map projection was geographic WGS84 which made the latitude line correct 1 minute = 1 nm. However when you measure on a navigation chart you use the Longitude line not latitude. I switched to NA Equidistant Conic projection which brings longitude closer but still falls short of my desired accuracy. This area is in the Pacific USA/MX area.
Any recommendations?
L

#2
Hans van der Maarel

Hans van der Maarel

    CartoTalk Editor-in-Chief

  • Admin
  • PipPipPipPipPipPipPip
  • 3,888 posts
  • Gender:Male
  • Location:The Netherlands
  • Interests:Cartography, GIS, history, popular science, music.
  • Netherlands

I'm working on a map/chart printout of points and lines with a latitude and longitude overlay and need my customers to be able to use the scale bar (in nautical miles) and longitude line to measure nautical miles. My first map projection was geographic WGS84 which made the latitude line correct 1 minute = 1 nm. However when you measure on a navigation chart you use the Longitude line not latitude. I switched to NA Equidistant Conic projection which brings longitude closer but still falls short of my desired accuracy. This area is in the Pacific USA/MX area.


Definately an equidistant projection. If your area of interest is larger N-S than E-W the Sinusoidal projection, centered somewhere in your area of interest, could be a useful one.

Do keep in mind that your users will be measuring with a margin of error, depending on the scale your map is at this may result in measurements being many many miles off. The accuracy is therefore not totally depending on your map.
Hans van der Maarel - Cartotalk Editor
Red Geographics
Email: hans@redgeographics.com / Twitter: @redgeographics

#3
Dennis McClendon

Dennis McClendon

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,084 posts
  • Gender:Male
  • Location:Chicago
  • Interests:map design, large-scale maps of cities
  • United States

I thought nautical charts generally used a Mercator projection so that compass headings could be easily plotted. So I have to wonder if the accuracy of distances is more important to the users than being able to plot courses along a straightedge. You don't say how big an area you're covering, but for a chart covering less than 100 x 100 km it's my understanding that the difference between projections is not much more than the paper stretches on different days. With GIS it's easy to introduce a precision that may not exist in the data.
Dennis McClendon, Chicago CartoGraphics
chicagocarto.com




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->