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Clustered in Space and Time with Background

I found a neighbourhood in northeast Calgary with both examples. The blue lines are the cast iron mains from the late forties; the green lines are PVC mains that were installed as replacements about 1990. The grey stars show the now-obsoleted breaks on the mains they replaced, with the year beside them. The coloured stars are the very few still-live breaks on surrounding mains that are still nowhere near to needing replacement 25 years later.

© Roy Brander, P.Eng 2016