First, the line of cross section on the map is assigned elevation values based on the underlying DEM and then converted into a route so that every vertex stores an X, Y, Z, and M attribute (Figure 2). Linear referencing is used in the cross section extension, in three ways. When the table of events is referenced to the route, a new feature class is created without requiring the user to know or calculate the XY coordinates of the new features. In a transportation-based GIS, a table of point events might represent the locations of bus stops along a bus route, and a table of line events might represent sections of a road network that are under construction. The second component is a table of point or line вЂњeventsвЂќ that occur along that route. The first is a вЂњrouteвЂќ, that is, a line feature that has been вЂњmeasuredвЂќ so that every vertex stores not only the X and Y attributes of its position but also a value, M, related to its distance from the starting point of the line. There are two intrinsic components to linear referencing. Cross section line in map view, above a geology polygon layer with boreholes.ДЄ key concept employed within this extension is that of вЂњlinear referencingвЂќ, a concept likely to be unfamiliar to most GIS users who have a geology backgrounde, as it was primarily designed to manage transportation systems.

The output data are stored within either ESRI shapefiles or ESRI geodatabase feature classes, depending on the format of the input layers.ДЇigure 1. A surface profile is interpolated from the DEM, apparent dip is calculated for structural measurements, boreholes are shown as stick columns, and the amount of vertical exaggeration can be controlled. In this paper, I describe a Visual Basic extension to ESRIвЂ™s ArcGIS program that takes relevant information from a geologic map-the digital elevation model (DEM), geologic polygon layer, structural point measurements, and borehole information (Figure 1)-and builds a template from which the user can begin to digitize a geologic cross section. Furthermore, with the introduction of the Environmental Systems Research Institute (ESRI) geodatabase format, it is possible to store the map and the cross section within the same data container, which simplifies distribution and archiving.

Features can be richly attributed and symbolized with the same symbology as in the map, the scale of the cross section can be more closely controlled than in a graphics program, and, once created, it is possible to project the cross section back into the coordinate system of the map with elevation values so that it could be used for 3D analysis or viewing. Yet, there are several advantages to creating cross sections within the same GIS as the map. While geologic maps are now almost always created within a geographic information system (GIS), geologic cross sections still are commonly portrayed and archived as simple un-attributed graphics in either paper form or digital files.

Geological Survey, 4200 University Ave., Anchorage, AK 99508 Creating and Managing Digital Geologic Cross Sections within ArcGISД«y Evan Thoms U.S.

Arcgis cross section tool from dem