I can understand your questions as both terms are not well known/used.

A Polish depth finder is a method for those without electronics to set their
fly depth precisely in relation to the bottom. Take a small bell sinker with
the brass swivel down the center. Pinch the swivel so it will JUST barely
admit the hook. Hook it on your lower fly (if you use a two fly rig) and lower
to the bottom. The leader will go slack just as you hit bottom. Grab the
waterline and pull up 12-18". Then grab the waterline again and set/peg
your bobber at that point. Your chiornomid will be the distance off bottom
that you set for that anchor drop. Do the same when you change location.

Bathometric maps are topographic maps of the lake bottoms. They are obtainable
here or from "Lakes of Washington" a book published by Dept of Ecology and
probably various other sources.
They are invaluable to locate areas of gently sloping bottom needed for good
chironomiding. When fishing areas of steep bottom your setting is invalidated
when you bobber drifts a short distance toward or away from shore.