What constitutes a GIS layer?

A GIS layer is fundamentally a dataset that represents a specific theme or subject matter, such as land use, transportation networks, or elevation. Each layer in a GIS serves to encapsulate and organize spatial data pertaining to that theme, allowing it to be analyzed in relation to other layers.

For example, in urban planning, one layer may represent population density, while another might depict zoning classifications. When these layers are combined, they enable planners to visualize and analyze the relationships between population distribution and land-use regulations effectively.

This thematic approach is crucial because it allows users to overlay different datasets and gain insights that are specific to those themes, thereby facilitating better decision-making and analysis in various fields that utilize geographic information systems. Other options provided do not adequately capture the essence of what a GIS layer represents in the context of spatial analysis and thematic data representation.