How do I know which PCS is most appropriate to project to?

Question

Hello!

I have a list of shapefiles that I am trying to merge together to create one larger shapefile. The issue here is that these shapefiles have different coordinate systems. The list below identifies all the different datums and coordinate systems I am working with. The top of each category in bold is the Datum followed by the italicized Geographic Coordinate system in that datum and the underlined Projected Coordinate System used with that particular datum and GCS. "NA" refers to no PCS used with that particular GCS in that Datum. Would anyone with expertise working with coordinate systems be able to suggest one PCS that would be best to batch project to?  I am most interested in polygon areas of these shapefiles so once I merge them I will need to calculate geometry to calculate the area of each polygon within the shapefile and I believe a PCS is necessary in order to do this. I am having trouble figuring out which PCS would be best given what I have below and if it is even possible to choose just one PCS given the different coordinate systems I have here. Any advice, info or tips would be great!

Row LabelsCount of GCSCount of PCSD_SIRGAS33GCS_SIRGAS33      SIRGAS_UTM_Zone_21S11      SIRGAS_UTM_Zone_23S22D_SIRGAS_200077GCS_SIRGAS 200077       NA11      SIRGAS_2000_UTM_zone_22S55      SIRGAS_UTM_Zone_22S11D_South_American_196911GCS_South_American_196911       SAD_1969_UTM_Zone_22S11D_South_American_Datum_1969_9611GCS_SAD69(96)11        SAD69_96_UTM_zone_23S11D_WGS_19844848GCS_WGS_19844747        NA3232       WGS_1984_UTM_Zone_22S1111       WGS_1984_UTM_Zone_23S44LL8411         NA11SA19691414LL-SA691414        SAD_1969_UTM_Zone_22S99        SAD_1969_UTM_Zone_23S44        SIRGAS_2000_UTM_Zone_23S11SIRGAS22SIRGAS22         SA_SIR_22S Transverse Mercator11         SA-SIR-22S11User Defined22South_American_Datum_1969_/_Geographic22   South_American_Datum_1969_/_UTM_zone_22S_(CM_51W)22

Thanks,

Melissa

MelitaKennedy · Answer

They probably needed a geographic transformation. Do you know if one was set? I would try re-doing them but making sure that a transformation is set. You could check this by adding the SA equal area conic PCS data to ArcMap, add the WGS84 data and set a transformation. You should get a warning message.The warning dialog has a button that links directly to the transformation dialog. If you don't get the warning after adding the WGS84 data, open data frame properties, select the Coordinate Systems tab and click the Transformations button.

MelissaTraverso · Answer

Hi Melita,

I have noticed that all shapefiles that were a south american PCS or GCS are okay but from a few checks the shapefiles that just had a GCS WGS 1984 are all slightly skewed when batch projected to South American Equal Area Conic PCS. Is there a way to fix this or batch re-project?

MelitaKennedy · Answer

Possibly--is the road very straight at that point? What could be happening is that the line should have a few more vertices in it. That is, the shape of the line should change with the reprojection, but isn't.

Melita