Datum transformations help you to more accurately re-project a GIS dataset from one coordinate system to another. Selecting an appropriate datum transformation is a stumbling block for many GIS users when they mashup datasets that use different coordinate systems.
Esri ArcGIS Desktop and Pro software have a robust project-on-the-fly system, however it’s worth taking a look at the datum transformation method the next time you’re adding a new dataset that uses a different coordinate system than your map’s.
Here at RIGIS, we’re continuing to use Esri’s “NAD_1983_To_WGS_1984_5” datum transformation when projecting data between Rhode Island State Plane NAD83 U.S. Survey Feet (EPSG 3438) and coordinate systems that use the WGS84 datum, such as Web Mercator WGS84 meters (EPSG 3857).
Here’s an example for how to go about selecting this datum transformation using ArcGIS Pro:
First confirm your your map’s coordinate system by first selecting your map’s properties window:
Next, select Coordinate Systems on the left, and select NAD 1983 StatePlane Rhode Island FIPS 3800 (US Feet) from the Projected Coordinate System / State Plane / NAD 1983 (US Feet) category:
At this point, you may also select Transformation on the left, and choose the NAD 1983 to WGS 1984 5 datum transformation.
As you add other datasets to your map, pay attention when the software prompts you for a datum transformation. The datum transformation you select may very well impact how accurately the datasets overlay on top of each other.
Additional Help Resources from Esri
Choosing an appropriate (datum) transformation
How To: Select the correct geographic (datum) transformation when projecting between datums
How To: Apply a geographic (datum) transformation in ArcMap
ArcGIS 10.6.1 and ArcGIS Pro 2.2 Geographic and Vertical Transformation Tables