#Surveyors, #landscapers, #architects and #geomap people, plus general tech nerds, I need your help!

I have to make a map of a 4 acre community centre premises with buildings, gardens, sports court, outdoor furniture, playground etc.

I am looking for some kind of IPhone app where I can walk the perimeter of the various fixtures to measure them and output the resulting lines into an image file. At minimum. Feels like this is a thing that would exist because fitbit and other locomotion tracking capabilities but I don't even know what I should search for to find such a thing.

Boost appreciated!