1. 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

2. Rasters

3. 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

4. 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

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

6. 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

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

8. Resolution & Scale

9. 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

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

11. 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

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

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

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

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

16. National Elevation Dataset
Terrain Modeling

17. National Land Cover Dataset
Land Classification

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

19. National Land Cover Dataset
Landsat 8 & 7
Multispectral ( Infrared- UV)
New data every 8 days

20. National Land Cover Dataset
Every ~ 5-10 years

21. Discussion
When we meet