Rasters Peter Fox – based on materials from Steve Signell GIS in the Sciences ERTH 496X Rasters Peter Fox – based on materials from Steve Signell Rensselaer Polytechnic Institute September 2016

Rasters

Rasters are tesselations A tessellation is a partition of space into mutually exclusive cells that together make up the complete study area There are two groups of tessellations: Regular tessellations, the cells are the same shape and size Irregular tessellations, the cells vary in shape and size

Regular tessellations All regular tessellations have in common that the cells are of the same shape and size, and the field attribute value assigned to a cell is associated with the entire area occupied by the cell Reality Regular tessellation

Irregular tesselations Triangulated Irregular Networks (TIN) Each plane fitted through three anchor points has a fixed gradient (Slope)

Two major types of raster data: Continuous Discrete, or ‘thematic’ Raster types Two major types of raster data: Continuous Discrete, or ‘thematic’ National Elevation Dataset (NED) National Land Cover Dataset (NLCD

Resolution & Scale The size of the area that a single raster cell represents is called the raster’s resolution Independent of scale

Resolution & Scale

Zones & Regions Zone: Any two or more cells with the same value belong to the same zone Region: Each group of connected cells in a zone is considered a region

Continuous Rasters Digital Elevation Model (DEM) National Elevation Dataset (NED)

National Elevation Dataset primary elevation data product of the USGS Seamless for US and territories Compiled from contour maps, remote sensing: SRTM, LiDAR, and more

National Elevation Dataset USGS contour maps Resolution: 10-30m Not empirical Quality varies by surveyor/map

National Elevation Dataset Shuttle Radar Terrain Model (SRTM) Resolution: 30m Holes

National Elevation Dataset LiDAR (Lilight, DARradar) High Resolution (sub cm) Multiple returns

National Elevation Dataset Updated regularly to reflect better data, changes in the landscape

National Elevation Dataset Terrain Modeling

National Land Cover Dataset Land Classification

National Land Cover Dataset NLCD derived from Landsat, a series of multi-spectral remote sensing satellites.

National Land Cover Dataset Landsat 8 & 7 Multispectral ( Infrared- UV) New data every 8 days http://landsat.usgs.gov/gallery.php

National Land Cover Dataset Every ~ 5-10 years http://www.mrlc.gov/ http://landcover-modeling.cr.usgs.gov/index.php

Discussion When we meet