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CONTOURS TECHNICAL SPECIFICATIONS

CONTOURS FROM STEREO IMAGERY

Contours offered as a value-add to Sanborn Standard and Enhanced Ortho products are:

  • 2-foot Contours – Derived from 4-inch or 6-inch resolution Sanborn Ortho
  • 5-foot Contours – Derived from 12-inch resolution Sanborn Ortho

Contours from stereo imagery are aesthetically pleasing and 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.

Every fifth contour line is an Index Contour, 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.

CONTOURS FROM LIDAR

Contours offered as a value add to Sanborn Lidar products are:

  • 1-foot Contours – Derived from Sanborn High Density Lidar
  • 2-foot Contours – Derived from any Sanborn Lidar

Contours are derived from a bare earth DEM surface, these contours best represent the high point density benefit of Lidar data. As an option, breaklines 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.

Every fifth contour line is an Index Contour, 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.

Accuracy statement

Sanborn contours are developed in accordance with the ASPRS contour guidelines for 1-foot, 2-foot, and 5-foot contour generation, and tested in accordance with NDEP-FEMA Appendix A guidelines. Accuracy testing in accordance with NDEP Version 1.0 May 10 Section 1.5.2.3 and 1.5.3.1 Fundamental Accuracy.

NMAS
Equivalent Contour Interval		 NMAS
VMAS 90 Confidence		 NSSDA
RMSEz		 NSSDA
Accuracy 95%
1-foot 0.5-foot .30-foot or 9.25 cm 0.60-foot or 18.25 cm
2-foot 1-foot 0.61-foot or 18.25 cm 1.19-foot or 36.3 cm
5-foot 2.5-foot 1.52-foot or 46.3 cm 2.98-foot or 90.8 cm

Technical Specifications

Relationship between Horizontal Resolution and Vertical Accuracy (ASPRS 2001) NDEP Section 1.3.8.2

Map datasets compiled at 1″ = 100′
with 1′ contours: Comparable to DTMs with post spacing of 1 meter.		 Map datasets compiled at 1″ = 200′
with 2′ contours: Comparable to DTMs with post spacing of 2 meter.		 Map datasets compiled at 1″ = 500′
with 5′ contours: Comparable to DTMs with post spacing of 5 meter.

Sanborn LogoFor more information or to order Sanborn Contours products or services, call Sanborn customer service at 1.866.SANBORN (1.866.726.2676), or contact us by e-mail at information@sanborn.com.