AbstractThis paper presents a study of free-standing Bronze Age megalithic monuments across western Scotland: Argyll, Lochaber, Kintyre, and the isles of Mull, Coll and Tiree. The original project was designed to unearth the locational choices of their builders, the reasons for these choices, and what they reveal about the belief systems of these societies. Using statistical analyses and 2D and 3D GIS, it will be demonstrated that vision is the main force behind locational decisions. The GIS analyses revealed that the builders chose a particular horizon shape, defined by qualities of distance, direction and relative apparent height as viewed from the monument (altitude). Significantly, approximately half the sites have the same locational variables as all the sites considered on the isles of Coll and Tiree (labelled ‘classic sites’: Higginbottom et al. in J Archaeol Method Theory 22:584–645, 2015.10.1007/s10816-013-9182-7), while the other half are the topographical reverse (‘reverse sites’), where the major ‘astronomical show’ differs due to the topographical differences between the site types. It is relevant to note that landscapes that block views of particular major astronomical phenomena in the south are significantly more common at reverse sites than at classic sites. Specific results pertaining to individual areas will also be highlighted. It will be seen that the interplay between the astronomy and the topographical choices of the builders at each site highlights possible cosmological ideologies that can be observed and that were shared across western Scotland.