2013 Lidar DEM: St. Johns County, FL

St. Johns County, Florida (County) has developed a comprehensive countywide base mapping and GIS enhancements to support master drainage planning, transportation planning, and preliminary engineering and wetland preservation studies. As part of this effort, Woolpert was contracted by Jones, Edmunds & Associates (JEA) to develop the new imagery and new DTM. The project consists of new 6-inch 4-Band Orthoimagery, new 1-meter max LiDAR, new 1-foot contours, updating of topographic/planimetric features. This data set is one component of a digital terrain model (DTM) for St. Johns County. The dataset is comprised of mass points, 2-D and 3-D breakline features, 1-foot and 2-foot contours, ground control, vertical test points, and a footprint of the data set, in the ESRI ArcGIS File Geodatabase format. In accordance with the counties specifications, the following breakline features are contained within the database: closed water bodies (lakes, reservoirs, etc) as 3-D polygons; linear hydrographic features (streams, shorelines, canals, swales, embankments, etc) as 3-D breaklines; coastal shorelines as 3-D linear features; edge of pavement road features as 3-D breaklines; soft features (ridges, valleys, etc.) as 3-D breaklines; island features as 3-D polygons; concretedam, culvert, footprint, lowconfidence, lowconfidenceanno, overpass, pipe, roadcenterlineoverbridge and swamppoint as 2-D features. Contours were generated from LiDAR ground class and breaklines and meet National Map Accuracy Standards. The LiDAR masspoints are delivered in the LAS file format based on the Florida statewide 5,000' by 5,000' grid. The GEOID model used to reduce satellite derived elevations to orthometric height is GEOID12A. Breakline features were captured to develop a hydrologically correct DTM. The coastalshoreline has a constant value of -0.6’ that was statistically derived from the LiDAR point cloud collected within the 2-hour window of MLL tide. 2008 Hydrographic and soft features were used to supplement the 2013 breaklines in Low Confidence areas.

The NOAA Office for Coastal Management (OCM) received the 5ft DEM data from St. Johns County GIS in March 2018 and processed the data to be available for download from the Data Access Viewer (DAV) and via https.

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available. These data are available for custom download at the link provided in the URL section of this metadata record.

Planimetric and breakline data are also available. These data are available for download at the link provided in the URL section of this metadata record. Please note that these products have not been reviewed by the NOAA Office for Coastal Management (OCM) and any conclusions drawn from the analysis of this information are not the responsibility of NOAA or OCM.

The DTM was created to support the development and maintenance of the St. Johns County Countywide Digital Contour Mapping Project. The project includes 6-inch color and IR countywide imagery. Breaklines improve the digital elevation model in areas where the point density is insufficient.

Project Title: ST. JOHNS COUNTY, FL Vendor Name: Woolpert, Inc.

The St. Johns County GIS Division provides this data "as is" and makes no warranties, expressed or implied, concerning the accuracy, completeness, reliability, or suitability of this data for any particular use or purpose. St. Johns County assumes no liability whatsoever associated with the use or misuse of such data.

Any conclusions drawn from the analysis of this information are not the responsibility of St. Johns County, NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

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Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1

Compiled to meet 1.2 feet (0.37 m) horizontal accuracy at 95% confidence level as defined by the FGDC Geospatial Positional Accuracy Standards, Part 3: NSSDA. LiDAR system calibration is available in the MTS Report of Specific Purpose Survey.

Vertical accuracy of the bare earth lidar is +/- 0.23-foot (7 cm) RMSE for unobscured ground points. The accuracy assessment was performed using a standard method to compute the root mean square error (RMSE) based on a TIN comparison of ground control points and filtered LiDAR data points. Filtered LiDAR data has had vegetation and cultural features removed and by analysis represents bare earth elevations. RMSE was used to compute the vertical accuracy based on methods described by the National Standard for Spatial Data Accuracy (NSSDA). The accuracy assessment was performed using a standard method to compute the root mean square error (RMSE) based on a comparison of ground control points and filtered LiDAR data points.

This LiDAR data represents the complete set of data for St. Johns County.

All formatted data are validated using commercial GIS software to ensure proper formatting and loading prior to delivery.