I would like to produce maps showing multiple lines that are in the same location.
This poses the problem that the lines overlap each other making one of multiple lines visible when displayed in a map.
Is there a method of making all the lines visible but keeping their location.
Best Answer
This question is a well known cartographic problem, and there are several ways to implement:
1) Offset. Like the underground/tube maps of cities, lines running o same set of tracks appear next to one another, like these example in NYC. This is only applicable if you have a limited number of overlapping lines.
2) Color-based. Changing the color of the feature based on density/intensity/overlap of features, like this example of underwater cables.
3) Symbol-based. as @recurvata suggested, you can change the symbol of overlapping lines by changing the thickness based on number of overlapped lines. Though line thickness in this map corresponds to volume, it can also be used for sum of overlap.
There isn't a definite answer to the best practice here, it all depends on your needs and message the maps you produce purvey.