Ross Custom Switches (www.rossswitches.com/technical.aspx) provides templates for every piece of track they sell. If your tablet connects to a printer, you can print whatever you need to use. To my knowledge, no available software works on a tablet. Only other choice is paper and pencil.
Ross templates come full size, which is handy for planning in 1:1. Not so much for scaled-down layout diagrams. I had my print shop print full size all the Ross switch and crossing templates I might ever use. I then colored the rails in with dark markers to make them easier to see, and then had them scanned again full size (so I would always have colored in rails).
I had those colored/scanned files then printed out in 1:12 size which gave me easy to see tiny switch templates. I made some curve templates in 1:12 size from styrene. I can now photocopy a bunch of the 1:12 switch templates and use my styrene curve templates to draw out track plans.
For paper, I use 1" square graph paper which can be purchased in pads that are 24"x32" in size (such as on Amazon if you search for "School smart chart table pad 24 x 32 inches, 1 inch grids, 25 sheets, white") for about $9. This means I can plan layouts that 12 in theory 24' x 32' big, though most of my doodlings are much smaller.
Once you have the templates made (which cost about $50 total for the printing, coloring, and scanning) you can do whatever you want with them.
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