Here are two paintings by Tom Thomson which demonstrate how he went from a field sketch to a finished painting. He changes the aspect ratio a bit but it’s blown up roughly 3.5 times in the final work.
“The Opening of the Rivers: Sketch for ‘Spring Ice’” (1915)
oil on wood-pulp board21.6 x 26.7 cm (8.5X10.5 in)
“Spring Ice” (1916)
oil on canvas72 x 102.3 cm (28.3X40.3 in)
Both are owned by the National Gallery of Canada, http://national.gallery.ca/ and displayed on http://cybermuse.gallery.ca/.