Thanks very much for any pointers.
You can construct a geoshape from a geopoint question in a repeat using the sum() function. You could populate each geopoint either by placing it on the map or calculating it based on coordinate questions. The coordinates need to be space-separated latitude and longitude values in decimal degrees. See attached for an example.
The Lines and Polygons sample available under Esri Samples in Conenct also has some examples of calculating a geoshape with a series of coordinates.