Do you mean you have a raster file and you want to create a vector file?
You can have a look at Utils.GenerateContours: http://www.mapwindow.org/documentation/mapwingis4.9/class_utils.html#af73b71167114bfcfb241c9b82a3f24b2
You can have a look at Utils.GenerateContours: http://www.mapwindow.org/documentation/mapwingis4.9/class_utils.html#af73b71167114bfcfb241c9b82a3f24b2