charly_

Geographic vs. projected coordinate system

Discussion created by charly_ on Sep 21, 2014
Latest reply on Feb 21, 2018 by geo2geog

Hi, I would need to deliver a result shapefile in WGS 84 (GCS: Geographic –lat/lon- coordinate system), the shapefile is originally in WGS84; but in the process of creating this result shapefile I need:

  1. To measure areas (the ArcGIS Calculate geometry tool doesn’t allow calculating areas with the Data frame coordinate reference system set to a GCS)
  2. To give raster resolution in meters, for example in the Cell Size attribute of the Polygon to raster conversion tool. It must be entered in degree units, what means that I have to make a conversion between degrees and meters, which is not accurate.

 

Then, the corresponding solutions I find in ArcGIS, and associate doubts, are:

  • set the Data Frame coordinate system to a proper projected coordinate system for that zone,
  • work with the shape layer, in WGS 84 (GCS) whereas the Data frame is in a Projected coordinate system,
  • once finished working and obtained the result shape layer: Export the shapefile by doing Data > Export Data and , for the option “Use the same coordinate system as:”, choose “this layer’s source data”.

 

The doubts are these: 

  1. Is it possible to make an accurate area measurement in a layer in meters, hectares, acres, etc, when the layer’s coordinate reference system is a GCS (though the Data frame has a projected coordinate reference system defined)?
  2. When doing in the result shapefile (in WGS 84) Data > Export Data and, for the option “Use the same coordinate system as:” choosing  “this layer’s source data”, is the resulting .shp going to be fully operative and to keep its geographic coordinates unmodified even if the Data frame coordinate reference system is a projected one?
  3. When creating a raster from a polygon, the raster is created in the projected coordinate reference system of the data frame. I need to deliver this raster (previously converted to polygon) in WGS84 (GCS); then, by doing the procedure

 

          * Change the Data frame coordinate reference system to WGS84, and

          * On the result raster, do Data > Export Data and, for the option “Use the same coordinate system as:”, choose “the data frame”,

 

is this an accurate way of dealing with that? I mean, aren’t there modifications in areas or coordinates of the delivered shape layer?

 

Thanks for any advice or idea.

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