Why? It will very unlikely come up as it came up in 2015 and a sketch map on an OS map came up in 2014 and a sketch of an aerial photograph came up in 2013. So why would you want to know if it's more than likely not going to come up?
is it no divide the length and width by 2 to get the dimensions for you're sketch map and then divide this box into 3 both horizontally and vertically. Also always put a title e.g. 'Sketch map of Killarney'. Also always put a key/legend under your sketch map when done.
I never do any of that ^ hahaha (except put a title). I just look at the map or photograph and assume the length & width of it and draw it. I never put legends or keys, I just label my sketched features.