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I have to choose a equal area projection for the country of Columbia and modify the central meridian and two standard parallels. I am using the South America Albers Equal Area conic projection.

I know how to go in a modify the parallels but how do I chose which standard parallels and central meridian to use?

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If you are using ArcMap, have a look at the tool Calculate Central Meridian And Parallels.

Calculates the central meridian and optional standard parallels based on the center point of a feature's extent; stores this coordinate system as a spatial reference string in a specified text field; and repeats this for a set, or subset, of features. This field can be used with Data Driven Pages to update the data frame coordinate system for each page.

You will find the central meridian and parallels in the generated spatial reference string. The String will look something like this:

PROJCS["South_America_Albers_Equal_Area_Conic",GEOGCS["GCS_South_American_1969",DATUM["D_South_American_1969",SPHEROID["GRS_1967_Truncated",6378160.0,298.25]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Albers"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-73.0915470244631],PARAMETER["Standard_Parallel_1",-0.6208706728606269],PARAMETER["Standard_Parallel_2",8.286527734396916],PARAMETER["Latitude_Of_Origin",-32.0],UNIT["Meter",1.0]]

Before you run this tool, you have to add a new text field to the feature class. Make sure that your feature class is in a Geodatabase since you need to set a high number (e.g. 1000) for the field's text length.

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