This is seems like an easy question to answer but for some reason I can't get the line shapefile that I've made to include m-values. I'm creating lines to map out the center of the river which I'll eventually use When creating the shapefile, I choose "Polyline" and check for the coordinates to include M-values. I then go about to make my line using the Editing tool, use the Smooth tool, and then use the Create Routes which should append M-values to my line shapefile. However, when I do this, it usually gives me M-values of NaN or no value at all.
How do I make it so that my line has M-values? I've also played around with my line shapefile where I've edited it so that the line is split at each vertex, and I will get a "Shape_Length" field with lengths of each segment. Are these "Shape_Length" values equivalent to M-values and used as M-values?
I'm a novice when it comes to ArcGIS so any help would be greatly appreciated