In ArcGIS Pro I need to determine the horizontal distance of a polyline, both in terms of straight line distance and then also the surface distance. Is the Shape_Length attribute always measuring straight line distance? How can I best then determine the surface distance of the polyline over my DEM?
If you have the 3D Analyst extension
Add Surface Information (3D Analyst)—ArcGIS Pro | Documentation
The Profile (Ready to Use) webtool will do this for you - it will provide geodesic length and straight line length.