Sanborn Contour products are highly accurate lines of equal elevation which are intended to correspond to the orthometric heights of the bare-earth surface.
Improvements in aerial data acquisition have increased the accuracy of modern maps while helping to reduce the time needed for precise mapping. Today, aerial acquisition is used extensively to supplement ground surveying as much larger areas can be mapped more efficiently than through conventional survey methods. Topographic mapping reveals the relief of an area by means of contour lines that represent elevation values; each contour line follows the geographical terrain while maintaining a constant elevation.
Sanborn offers two types of contour products, each at varying technical specifications which are relative to the acquired digital terrain model (DTM):
Contours From Stereo Imagery
Contours Products offered as a value-add to Sanborn Standard and Enhanced Ortho Products are:
2-foot Contours
Derived from 4" or 6" Sanborn Ortho Products
5-foot Contours
Derived from 12" Sanborn Ortho Products
Sanborn Contours from stereo imagery are aesthetically pleasing, highly accurate lines of equal elevation which are intended to correspond with the orthometric heights of the bare surface. The primary advantage of stereo imagery is the ability to extract cultural and geographic features in three dimensions such as buildings, roads and elevation contours. Stereo imagery is especially important for markets where accurate elevation data is not readily available.
Contours From LiDAR Data
Contours offered as a value add to Sanborn LiDAR products are:
1-foot Contours
Derived from Sanborn High Density LiDAR Product
2-foot Contours
Derived from any Sanborn LiDAR Product
Sanborn contours from LiDAR data are derived from a bare-earth DEM surface. These contours best represent the high point density benefit of LiDAR data. As an option, break lines can be added to better depict edge of drainage feature, road edges and other sharp breaks or discontinuities in the terrain. Contours from LiDAR are normally not smoothed, leading to a ragged appearance, this is not as cartographically as pleasing, however best represent the highly detailed surface. A gridding of the bare earth and smoothing can be applied at customer request to create a more traditional looking contour data set but reduces accuracy overall as a result.
For all contours products, every fifth contour line is an index contour and is distinguished using a heavier line style to enhance identification. All contour lines are solid and unbroken except where passing through dense ground cover, building, and under bridges. In these instances, the contour lines are still continuous, but they are attributed and displayed as broken/dashed lines.
Who benefits from Sanborn Contours?
The surface of the Earth is continuously changing on local, regional, national and global scales. Changes in terrain can have significant impacts for people, the economy and the environment. Organizations that benefit from the information derived from Sanborn Contours are:
State, local, and county governments
Land developers
Transportation
Engineering
Military
Commercial
Typical uses for Sanborn Contours
Sanborn Contours are used for planning land management applications such as:
Land development
Floodplain analysis
Route location
Emergency response
FEMA mapping
Coastal engineering
Storm water management
Disaster preparedness and respons
Water supply and qualit
Coastal engineerin
Land transportation and safety
Contours Products Sample Imagery--Click to Enlarge
Accuracy Statements
Sanborn Contours are developed in accordance with the ASPRS contour guidelines for 1-foot, 2-foot, and 5-foot contour generation, and are tested in accordance with NDEP-FEMA Appendix A guidelines.
NMAS
Equiv. Contour Int.
NMAS
VMAS 90 Confidence
1-foot
0.5ft
2-foot
1.0ft
5-foot
2.5ft
NMAS
Equiv. Contour Int.
NSSDA
RMSEz
1-foot
.30-or 9.25cm
2-foot
.61ft 18.25cm
5-foot
1.52ft - 46.3cm
NMAS
Equiv. Contour Int.
NSSDA
Accuracy 95%
1-foot
0.60ft 18.2cm
2-foot
1.19ft or 36.3cm
5-foot
2.98ft - 90.8cm
Accuracy testing in accordance with NDEP Version 1.0 May 10 Section 1.5.2.3 and 1.5.3.1 Fundamental Accuracy
Technical Specifications
Relationship between Horizontal Resolution and Vertical Accuracy (ASPRS 2001) NDEP Section 1.3.8.2
Maps compiled at 1" = 100' with 1' contours
Comparable to DTMs with post spacing
of 1 meter
Maps compiled at 1" = 200' with 2' contours
Comparable to DTMs with post spacing
of 2 meter
Maps compiled at 1" = 500' with 5' contours
Comparable to DTMs with post spacing
of 5 meter
Delivery Formats
.dwg (AutoCAD)
.dxf (Drawing Exchange)
.shp (ESRI)
For pricing and additional information, or to order Sanborn Contours Products, contact Sanborn customer service by phone at 1.866.SANBORN or send email to information@sanborn.com.
