1. In weather analysis and forecasting, a graphic representation of a vertical surface in the atmosphere, along a given horizontal line or path, and extending from the earth's surface to a given altitude. The type of data and analysis presented on such a cross-sectional chart depends upon its purpose. In meteorology, a synoptic cross section is prepared from synoptic weather data. In aviation, a flight cross section (or route cross section) is a graphic forecast of conditions expected to be encountered along the proposed flight route; therefore, time varies along the horizontal axis of the chart. Compare time section. 2. Generally, a two-dimensional, representative picture of a three-dimensional entity; usually a section or slice perpendicular to the principal axis of the entity, or passing through its center, or otherwise representative of a given aspect of the entity. See scattering cross section; compare profile, contour.