Episode #2.7 - S2-E7
Plot hole: The professor at the beginning of the episode says;"I want the instruments photographed as back-up", which makes total sense. And in fact we do see pictures of exactly that...except one. The one photo that will prove to be fatal for the murderer is a picture not of the instruments, but of the weather station, which would be absolutely useless as backup for being too distant. But had it been a close-up, the 'shadow' gimmick that solves the case would have not happened.
Episode #2.7 - S2-E7
Plot hole: It is established that there are 4 stations in the N, S, E, W parts of the island and it takes roughly the same amount of time to get to any of them from the central part of the island where the university is. When we see a map of the fictional Saint Marie as DI Richard Poole explains how he is going to look for the camera, the map shows an island with a distance W to E about double the the distance from N to S, making impossible that one could get by car to places with such different distance from the center in equal amounts of time. (00:30:50)
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
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