contourover

Contourover is a term used in data visualization to describe the practice of overlaying contour plots with other graphical representations, such as heatmaps, density plots, or scatter plots, to reveal relationships between variables in a single view. Although not standardized, contourover is used to convey both the shape of a scalar field and the distribution of a second variable, enabling analysts to compare patterns across layers without switching between plots. It can help highlight where high-density regions coincide with particular contour levels or where gradients align with geographic or experimental boundaries.

Techniques for effective contourover include selecting relevant contour levels that reflect meaningful ranges, applying transparent or semi-transparent contour layers, ensuring consistent coordinate systems and scales, and using perceptually uniform color maps to minimize confusion. Designers often adjust contour spacing, blending modes, and layer order to reduce clutter while preserving interpretability.

Applications span several fields. In meteorology, contour lines for temperature or pressure can be overlaid with precipitation or wind field visuals. In geosciences, elevation contours may be shown atop satellite imagery or soil property maps. In epidemiology and ecology, case density or habitat suitability contours can be combined with location data to reveal hotspots and trends. In engineering, stress or strain contours may accompany geometric outlines of components.

Implementation typically involves layering techniques available in common visualization tools. For example, a base plot such as a scatter or heatmap is created, then a contour or contourf layer is added with an alpha parameter to form the contourover. GIS software can render contour rasters atop base maps with transparency, enabling interactive exploration.

See also: contour plot, heatmap, overlay, GIS.