overlays

An overlay is content or data placed on top of another layer or surface, typically without altering the underlying material. In computing and digital media, overlays provide supplementary information, controls, or effects that coexist with the main content, and they can be semitransparent or opaque, interactive or static.

In user interfaces and graphic design, overlays include tooltips, pop-up dialogs, modal windows, captions, and decorative elements such as logos layered over images or video.

In maps and geographic information systems (GIS), overlay layers combine geographic data with thematic information, enabling analysis by intersecting or uniting features, for example a road network overlaid with land-use data.

In video and image processing, overlays provide subtitles, captions, logos, and animated graphics that appear on top of base footage or imagery.

In computing, the term also refers to overlay memory techniques, where a program is divided into segments that are loaded on demand to fit within limited RAM.

In networking, an overlay network is a virtual network built on top of another network, enabling new addressing, routing, or security properties independent of the underlying infrastructure.

Overlays are non-destructive and reversible, designed to extend functionality or information without modifying the original material. See also overlayFS, modal dialogs, and GIS overlay analysis for related concepts.