gp1870f plotter resolution

I am using a gp1870f in interior Alaska. we are doing work in a section of river about 1/2 mile by 1/4 mile and with the supplied world map, the maximum plotter resolution has a display width that is 5.6 mile.

I would like to plot positions within yards or 10s of yards. How can I increase the resolution?
-can I turn off the map and record tracks(the map is unnecessary for our work) ?
-do I need to purchase a C-Map for our area to obtain maximum resolution?

Try turning chart lock off.

Depending on if it functions with the base map it might allow you to zoom in further.
Spike