[mysterydip]

I would think you could do a scaling of sorts, like if your map was 100x100 you could reduce it to 10x10 with "clear", "fully blocked", and "partially blocked" based on the contents, and work a general path at that meta level first, then focus on each grid map at the full scale to navigate around local obstacles. You could do multiple scales depending on your needs and where the terrain makes sense to categorize most into clear or blocked.