Whether detail and overview share one view or split across two is what separates these two patterns

What it is

Focus plus context and overview-plus-detail both promise "detail and the whole at once"; the difference is a single geometric fact: the former holds both scales in one view, the latter splits them across two views (main view plus minimap, or large canvas plus overview window). That fact fixes their cost structures and the tasks they fit — selection means choosing between exactly these two.

Why it happens

Splitting or not splitting changes three cost lines: gaze cost — same-view comparison switches nothing, dual views commute on every check; space cost — the same-view pattern divides the canvas between focus and context (each yields ground), while dual views let each occupy a full canvas; implementation cost — transitions and distortion are complex in the same-view pattern, while dual views need only layout plus linking. The selection rules follow: frequent comparison with shallow detail depth favours same-view; deep detail needs (full resolution) or complex global maps (a full-size overview) favour dual views. Mature products use both — main view plus minimap is the dual pattern, tree collapsing is the same-view pattern — and the craft is landing each task on its cheaper mode.

Where it stops holding

The two are a continuum, not an exclusive pair: a minimap nested in the main canvas's corner sits between them (same canvas spatially, two views logically). The judgment stays a trade of comparison cost against space cost, not a formal count of windows. Screen size joins the selection: on small screens the space cost of dual views rises steeply, and same-view patterns (collapse, drawers) dominate mobile. Good linking also erodes the dual view's commute cost — tightly linked dual views (instant selection sync) approach the same-view experience, though the gaze travel remains.

Applying it

• Estimate comparison frequency and detail depth before designing: high-frequency shallow comparison takes the same-view mode; low-frequency deep detail takes the dual mode.
• Dual views must be linked (selection sync, mutual viewport indication) to squeeze the commute cost to its floor.
• Verification: have users complete the same comparison task in prototypes of both modes, timing and error rates compared; when the gap is significant, ship the cheaper mode.

Related

• Same group: U6.06.1 Focus plus context keeps detail and global in one view · U6.06.3 The transition between focus and context must be continuous and legible · U6.06.4 The pattern saves gaze switches but adds spatial comprehension load · U6.06.5 The focus position must be movable by the user
• Nearby: U6.02.1 A selection in one view should sync to related views · U6.04.3 Zooming must keep an exit back to the global view
• Search terms: overview plus detail · focus context comparison · minimap design