Did the same, no cloud, plotting on top of open street maps, automated logging.

Excerpt from the result (don't want to disclose where exactly I live): https://i.imgur.com/FPyRAkA.png

My setup for it:

   - andoid app tasker (checking if I loose wifi, in that case start GPSlogger)
   - android app GPSlogger does the logging, set to relatively coarse in hopes to save battery)
   - and visualize on my computer with this python script http://sethoscope.net/heatmap/ (with a custom gradient that has no transparency. I want to see where I've been just once too.

You can also render it on android with GPX Viewer but loading takes a long time once you got a bunch of tracks.

It's tough on your phones battery though. I think I pushed my aging one over the edge with it.