Footprint charts are like candlestick charts...on steroids, that is.
While candlestick charts are living in 2D; footprint charts are living in multiple dimensions. Rather than just tracking price, footprint charts include other dimensions of info, such as bid-ask spreads, liquidity levels, and volume.
Because technology is handy-dandy, investors can customize their own footprint charts to include the variables they want to look at...again, like a candlestick chart, but much, much more.
Welcome to the dark side.