Overall see three options for planning out where you are going to fly.
This assumes you want to fly the perimeter (linear flight mission) and not the entire area.
If you want to capture date of the entire area would want to plan out a 2d mapping mission based on a polygon instead.
Automation
If we want to automate linear data collection we want to have line(s) for us to build the automated flight plans from on the remote controller.
Pro: Consistent data capture, capture exactly what you want, reduce pilot fatigue.
Option A) Utilize existing GIS perimeter data that already exists of the fire
Pro: Most likely going to be very accurate
Pro: Easy to import data like a kml into flight software/Flight Hub 2
Con: May require additional post processing and smoothing before getting going
Con: Requirements to fly may change or may not be the same
Option B) Draw it yourself
Pro: Fairly smooth/easy to do if simply drawing a line around visible location(s) on a map like a house line or road.
Con: May not have the most up to date base map available so drawing may not be as accurate
Manual
Option C) Manually fly and adjust route with the drone based on what the pilot is seeing
Pro: Get going quickly.
Con: Higher pilot fatigue and requirement of knowledge of where to fly/able to interpret on the fly.