The district boundary lines, unless shown otherwise, are intended generally to follow street corner lines, railroad right-of-way lines, reservoirs, lakes or other bodies of water, watercourses, lot lines or boundaries of subdivisions or Town boundary lines or the straight-line projections of such lines, all as shown on the Zoning Map. Where a district boundary line does not follow such a line, its position is shown on the Zoning Map by a specific dimension expressing its distance in feet from such a street center line or other boundary line as indicated.