# Central Meridians and LCC

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07-19-2013 11:55 AM
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Occasional Contributor
This is a question that bugs me and I cant seem to find any good answers.  Does it matter where the central meridian/longitude of origin is placed when using  Lambert Conformal Conic?  I have heard yes and no, but have not found WHY?  It seems like it is best practice to have the central meridian, well, central, but could you just have it at the western most extent of the AOI instead of having a false easting?

Thanks.
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Esri Notable Contributor
Yes, you could move it to west of an area of interest. It will affect two things--the coordinate values as you realized (both x and y, as the 0,0 point before the false easting and northing are applied is at the intersection of the central meridian and the latitude of origin) and the rotation of the data. As the central meridian moves west, an area of interest will rotate counterclockwise and move 'right' and 'up' on a map.

Melita
2 Replies
Esri Notable Contributor
Yes, you could move it to west of an area of interest. It will affect two things--the coordinate values as you realized (both x and y, as the 0,0 point before the false easting and northing are applied is at the intersection of the central meridian and the latitude of origin) and the rotation of the data. As the central meridian moves west, an area of interest will rotate counterclockwise and move 'right' and 'up' on a map.

Melita
MVP Esteemed Contributor
Center you CM in the center of your extent if you want to use a non-standard LCC.  For example the CM for Canada is -96 degress longitude since it is in the middlish of Canada, but if you were working in BC or Nova Scotia, then it would be a useless CM hence, you would use a different longitudinal appropriate projection or move the CM accordingly.