Fix reference issue (check)
Fix reference issue (check)

majazaloznik/spatial-microsim-book,Robinlovelace/spatial-microsim-book,modumont/spatial-microsim-book,richardellison/spatial-microsim-book,majazaloznik/spatial-microsim-book,modumont/spatial-microsim-book,modumont/spatial-microsim-book,Robinlovelace/spatial-microsim-book,richardellison/spatial-microsim-book,Robinlovelace/spatial-microsim-book