(a)   Where boundaries are indicated as approximately following the center lines of thoroughfares or highways, street lines, or highway right of way lines, such center lines, street lines, or highway right of way lines shall be construed to be such boundaries;

   (b)   Where district boundaries are so indicated that they approximately follow the lot lines, such lot lines shall be construed to be said boundaries;

   (c)    Where district boundaries are so indicated that they are approximately parallel to the center lines or street lines of streets, or the center lines or right of way lines of highways, such district boundaries shall be construed as being parallel thereto and at such distance therefrom as indicated on the Official Zoning Map. If no distance is given, such dimensions shall be determined by the use of the scale shown on the Official Zoning Map;

   (d)   Where the boundary of a district follows a railroad line, such boundary shall be deemed to be located in the middle of the main tracks of said railroad line.