A topographic survey, also known as a “topo”, is a site map showing the elevation differences by the use of contour lines. Topographic features could include ditches, berms, hills and other natural features. The map may also include improvements such as buildings, utility locations, detention ponds, parking lots and other features which would affect engineering design on the site. Topographic contours can be shown at almost any interval that is specified by the client. The most common intervals used are 1 foot or 2 foot contours, meaning that a contour line will be used for every 1 or 2 feet of change in elevation.  The topographic map is prepared by gathering horizontal and vertical data from the site. For most sites, the use of a total station or GPS is sufficient for gathering of field data.  Once the raw data has been collected, it is downloaded into a computer program to create a digital terrain model to create the contour lines.  A topographic map is most often requested by engineers, architects or building contractors who need to know information about overall site grade and elevations. This information may be used to determine placement of site improvements, estimate the volume of dirt to be moved, or for many other construction and development purposes.