All topographic data products were collected and/or derived from a high-precision Lidar survey. All data products conform to guidelines and standards specified in the Florida County Option Orthoimagery Program Standards, 2018, USGS Lidar Base Specification 11-B4, ASPRS Positional Accuracy Standards for Geospatial Data, and Florida Statues, Chapter 472.
Breakline data was collected for use in producing digital elevation models (DEMs) and for hydrologic and hydraulic modeling. Hydrographic breaklines were collected to support hydrography-related requirements in the DEM. Single-line hydro breaklines were collected to enforce monotonic drainage. Area-based breaklies were collected for hydro-flattening the DEM for rivers and streams wider than 10 feet and for lakes and ponds greater than 0.25 acres. Hard and soft breaklines, along with bridge and saddle breaklines were collected for ensuring proper surface morphology. The breakline z-values were derived by point cloud interpolation.
Classified Lidar Point Cloud
A Lidar survey is collected countywide every three years. The latest was captured in 2018. The Lidar was collected to meet or exceed Quality Level 0 as specified in USGS Lidar Base Specification 11-B4 and ASPRS Positional Accuracy Standards for Geospatial Data. This requires that the data meet or exceed a non-vegetated vertical accuracy of 0.05 meters or 0.16 feet RMSEz and a minimum ground point density of 8 points per square meter . By using independent checkpoints, the vertical accuracy of the 2018 Lidar data was tested to meet 0.12 feet RMSEz in non-vegetated areas. The Lidar point cloud data was delivered in LAS 1.4 format and classified into the following classes: ground, low vegetation, medium vegetation, high vegetation, buildings, and water.
TA countywide set of 2-ft contours was produced from the DTM. The vertical accuracy of the DTM supports the create of half-foot contours as needed.
Digital Elevation Model
The Lidar ground points along with breakline data were used to produce a digital elevation model (DEM) with a spatial resolution of 2.5 feet. A hillshade model was derived from the DEM to facilitate shaded-relief mapping.
Digital Terrain Model
The Lidar ground points, breaklines, and the project boundary (Leon County) were used to create a triangulated digital terrain model surface (DTM). The DTM is stored in an ESRI LAS Dataset.
Classified LiDAR was used to create a Canopy Density raster, which represents the ratio of vegetation to ground as seen from above. A 5-ft resolution forest cover raster was generated from the Lidar point cloud using classes 5 and 6 medium and high vegetation respectively).
Spot elevations were collected at high and low points in the landscape and at road intersections.