# Central meridian in Lambert conformal conic distorting distance?

Does a different central meridian in Lambert conformal conic projection with two standard parallels make a difference in line length?

I have projected a line in GCS WGS84 TO Lambert conformal conic projection, with the standard parallel 1 = 09 and standard parallel 2 = 35. I have no idea what should be the central meridian.

The actual length is short in Lambert conformal conic projection system.

The actual Route from kathmandu to Delhi is asshown in figure below from skyvector.com and the distance is 460 nm ..............

I have drawn the same route in arcmap with in the following projection

GCS_WGS_1984 WKID: 4326 Authority: EPSG Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_WGS_1984 Spheroid: WGS_1984 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314245179 Inverse Flattening: 298.257223563

I created the following projected coordinate system according to jeppesen chart.

Asia_Lambert_Conformal_Conic_09and 35 Authority: Custom Projection: Lambert_Conformal_Conic False_Easting: 0.0 False_Northing: 0.0 Central_Meridian: 70.0 Standard_Parallel_1: 9.0 Standard_Parallel_2: 35.0 Latitude_Of_Origin: 22.0 Linear Unit: Meter (1.0)

Geographic Coordinate System: GCS_WGS_1984 Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_WGS_1984 Spheroid: WGS_1984 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314245179 Inverse Flattening: 298.257223563

Jeppesen chart with the projection system Highlighted in Red

I projected my line from WGS84 GCS to above Defined projected coordinate system and when I calculated the length of the line in ArcMap the line is 10 NM shorter than the actual one. I believe with the same projection as Jeppesen Chart, I should be able to get the length of line exactly as Jeppesen chart. I don't know where I am mistaken.

The difference in line length should not be due to the central meridian value UNLESS you have a very long line that is not densified. That is, the line has only end points, e.g., 2 points. A straight line in one coordinate reference system (CRS) (or "projection") may be curved in another CRS.

It's more likely that you see a difference in length because Lambert conformal conic maintains shapes and angles, not distances. Length distortion is the same in Lambert conformal conic along meridian lines, but changes as the latitude changes.

If the length is too short, I predict that the line is between the two standard parallels.

Update based on comments and revised Question, 25 September 2018.

I created a similar Lambert conformal conic PCS using 85 for the central meridian, 9 and 35 for the standard parallels. Using the Measure tool set to calculate planar distances and approximating the points of the flight path, I got 461.7 NM. If I use geodesic distance calculation instead, it's about 10 NM more.

• Dear mkennedy, Thank you for the response. I used the projection parameter exactly as defined in Jeppesen Chart but the projected distance is shorter than the actual one , I will try to elaborate the problem , i will edit my question so that you can see the real problem.
– JBB
Sep 25, 2018 at 9:19
• Thank You, it helped me alot ,I did the accordingly as you have mentioned, I created LCC using 85 for the central meridian, 9 and 35 for the standard parallels. But I got the Opposite Result , Measure tool set to Geodesic i got 461.7 NM but with the measure tool set to planar i got 10 NM less, Also Is there any tool that helps me calculate geodesic distance. Is it accurate to calculate flight routes in geodesic ?
– JBB
Sep 27, 2018 at 7:39