1. A diagram showing the spatial relation of elements in a vertical plane. 2. A geological diagram showing the formations and structures cut by a vertical plane. 3. A plot of seismic reflection events along a seismic line. Events are usually (but not always) migrated and the vertical scale is usually depth (but occasionally time). See plotted section. 4. A concept to represent the probability of collision between particles. A particle has to pass within a certain distance of another particle for the two to interact, the effective distance depending on the type of interaction. See capture cross-section.