DVD discs containing one foot cartographic contour data for Lake County are now available for purchase. These contour lines connect points of equal elevation at intervals of one vertical foot. The contours were developed using data collected in April - May 2007 using LiDAR, a laser technology to measure the distance from a specially equipped airplane to the surface of the earth to determine ground elevation. The contours are intended to correspond to the orthometric heights of the bare surface of the county (no buildings or vegetation cover). The use of LiDAR significantly reduces the cost for developing this information. Contour data is used by county agencies to study drainage issues such as flooding and erosion. Customers interested in the actual LiDAR data may download it at no cost from the USGS Center for LiDAR Information Coordination and Knowledge.
These data were compiled to meet the American Society for Photogrammetry and Remote Sensing (ASPRS) Accuracy Standards for Large-Scale Maps, CLASS 1 map accuracy.
The U.S. Army Corps of Engineers Engineering and Design Manual for Photogrammetric Production recommends that contour data intended for this usage scale be used for any of the following purposes: route location, preliminary alignment and design, preliminary project planning, hydraulic sections, rough earthwork estimates, or high-gradient terrain / low unit cost earthwork excavation estimates. The manual does not recommend that these contours be used for final design, excavation and grading plans, earthwork computations for bid estimates or contract measurement and payment.
This contour data does not take the place of an on-site survey for design, construction or regulatory purposes.
Each DVD contains 494 individual contour data files in ESRI shapefiles and also in the form of Autodesk AutoCAD Drawing Files (dwg) or Bentley Systems MicroStation Design Files (dgn) format. The tile scheme used for the contours is based on the approximate Public Land Survey System (PLSS) section lines, covering approximately one square mile plus an additional 100' buffer on each side (excluding those areas outside of the county borders and the area extending into Lake Michigan). They are not based on Public Land Survey System monument coordinates. Consult a professional Land Surveyor registered to practice in Illinois if true ground locations are needed.
The files provided are in the Illinois State Plane Projection, East Zone, and the HARN Horizontal Datum. The vertical datum is NAVD88. The units of measure are US Survey feet. Each DVD also includes metadata compliant with Federal Geographic Data Committee metadata standards.
Purchasers should verify that the software they plan to use with this data is capable of reading one of the following sample files Environmental Systems Research Institute (ESRI) shape files (shp) and/or Bentley Systems MicroStation v8i design file (dgn) and/or AutoCAD r2010 drawing file (dwg) before buying the DVD.
The price for each contour data DVD is $50 and includes the GIS shapefiles (shp) and one CAD format (dgn or dwg) for the entire county. The purchase price is not refundable. A defective disc may be exchanged for a replacement disc for the same product at no charge. Purchasers should verify that the software they plan to use with this data is capable of reading one of the sample files available above. No software is provided with the data on these DVDs.
The Spring 2007 digital orthophoto obtained in the same period as the LiDAR data is available on DVD and makes an excellent companion to the contour data. Although the contour data can be viewed with earlier or later digital aerial photography the surface of the land will not precisely match the contours due to such factors as new construction, demolition, road alignment changes, lake and stream erosion or restoration projects and other events. There is a high rate of change in the landscape in many parts of Lake County that may alter the elevation of the land.
Information about digital aerial photography available from the county may be found here.