In the following code:

extensions [gis ]
globals [boundary grandstands]


to setup
  clear-all
  ask patches [set pcolor white]
  set boundary gis:load-dataset "C:/Users/kma84/Work Folders/Documents/_pedestrian dynamics/Netlogo/Silverstone/boundary_project_2.shp"
  set grandstands gis:load-dataset "C:/Users/kma84/Work Folders/Documents/_pedestrian dynamics/Netlogo/Silverstone/grandstands2.shp"
;;  gis:set-world-envelope gis:envelope-of boundary
;;  gis:set-world-envelope gis:envelope-of grandstands
  gis:set-world-envelope (gis:envelope-union-of (gis:envelope-of grandstands) (gis:envelope-of boundary))
  gis:set-drawing-color blue
  gis:draw boundary 1
  gis:draw grandstands 1

end

the two shapefiles upload with no obvious problem. They are taken from the same canvas on QGIS. one is a lines (boundary) and the other polygons (grandstands).

enter image description here

If I have just one 'set-world-envelope' line and the corresponding 'draw' line, that file will show (say boundary or grandstands). But if I try to show both by having the union-of code plus 2 x draw codes nothing happens.

What might solve this?