The difference between 2-D and 3-D seismic lies in the number of vibrations from which meaningful information can be calibrated. With 2-D, geophones along a line of vibrations provided a picture that was a cross-section - a slice - of the rock formation. With 3-D, the geophones cover a grid, not just a line. With thousands of times more data points, scientists can map a cube, creating a 3-dimensional computer image of the formation. While 3-D is many times more expensive than 2-D, it allows companies to avoid unlikely prospects, and hence wasting money on unsuccessful wells. While seismic data has typically been collected with the sources and receivers in straight lines, 3-D seismic requires a much denser grid of trails than the 2-D seismic.