3D environments require 3D visualisations: the limitations of 2D sketch maps in capturing spatial knowledge

Sketch maps are a widely utilized method for assessing how participants encode and externalize knowledge of large-scale environments. Even though many such spaces include an important vertical component, participants tend to omit, or distort vertical information when drawing 2D sketch maps. Recent advancement in Virtual Reality sketching interfaces open the question whether sketch maps could be realised in 3D. We recruited participants across two experiments – one in a layered indoor environment, one in a volumetric urban environment – and assessed their 2D and 3D sketch maps by coding the occurrence and correctness of qualitative spatial relations across all three dimensions. Results show that when tasked with drawing vertically-complex spaces on traditional 2D pen-and-paper medium, participants omit a lot of (mostly vertical) information that they do in fact store in their cognitive model of that space and can externalise in a Virtual Reality-based 3D sketch map. This indicates that 2D sketch maps may be a bottleneck for expressing valid parts of participants’ spatial knowledge of vertically-complex spaces, while 3D sketch maps offer a promising alternative.