Imho many layers suffer from actually a quite huge range of values being mappen on a small amount of colors.
Often layers are like 90% green.
We can apply the above suggestions on weights and speed limits, but still it will be an issue to properly display the usual rail speeds properly, especially in periods of transition, which is where people are usually most interessted in detecting old infrastructure to set up upgrading.
There are only 10 color steps, of which some are quite hard to distinguish without a direct comparisation.
Currently, there are a tleast railway tracks of 50 km/h, 80 km/h, 120 km/h, 130 km/h, 145 km/h, 155 km/h, 160 km/h, 200 km/h, 225 km/h, 240 km/h, 300 km/h, 320 km/h around the map on stephenson-siemens.
That's already more than what we can differ using the current scale.
So my suggestion is a minimap setting where the player can influence the mapping.
For example, a min and max setting, where all values are clamped to the color scale is applied to that range.
That means, if we want to seek out for old 155 km/h tracks, to schedule replacement, we can set the range to something like min: 150, max:160,
so 150 and less will be red, 160 and greater will be green and 155 will be yellow.
I am aware, that different types of layers use different number ranges, thus specifying the range relative to the full range, rather than in absolute numbers might be sensible.
The issue of multiple layers might remain, but I am usually really interessted in the values of one of those layers a the same time, the other layers beinfg only of secondary importance, to better relate the primarily displayed data to what is going on there.
Passenger stops show coverage even without any service, perhaps walking is counted as service.
That's not an issue of the map but an issue of stop statistics and internal transfer times.
Internal transfer times are usually smaller than actually walking the same distance, thus passengers will walk to a stop "transfer" there, to walk to another stop and that's still counted as a successful journey.
You can try it out, simply placing an entirely unserved stop in a city. It will frequently report success nevertheless.
Alternatively, have a look at stephenson-siemens. For example Cheppike Manga High street ins entirely unserved. Still there are roughly 20 passengers on average using that stop successfully.
Note, that it has an internal transfer time of 0:54, but it takes 3:42 to walk to a diagonally adjacent tile.
That one is very difficult to circumvent as it's the result of graphics scale/economic scale. Walking times are calculated to economic scale, but transfer times are related to a fixed scale, which is roughly the graphics scale.
Edit: It happened again, after switching from a local stephenson-siemens save (my default save) to bridgewater.
See the attachment. The error doesn't make sense to me, however and I still don't know how to reliably reproduce. At least I got an idea.
Should I start a bugreport on its own?