WebMapViewer.Update
From Xojo Documentation
Method
Centers the map on the current Latitude and Longitude.
Notes
After making any changes to either Latitude or Longitude, you need to call the Update method for the map to update its location.
Example
Set the map to a specific latitude and longitude:
MapViewer1.Latitude = 38.8977
MapViewer1.Longitude = -77.0366
MapViewer1.Update
MapViewer1.Longitude = -77.0366
MapViewer1.Update