This document discusses raster data in GIS. Raster data represents geographic information as a grid of cells or pixels organized into a matrix of rows and columns. Each cell contains a value representing information such as elevation, vegetation index, or land use class. Raster data can represent data as integers, floats, or other data types and comes in various resolutions, with higher resolution providing more detail. Rasters can be single band (one value per cell) or multiband (multiple values per cell representing different wavelengths). Examples of raster data sources include remote sensing imagery, digital elevation models, and land cover maps.

1. Raster data
Dr. Hans van der Kwast
OpenCourseWare
ocw.unesco-ihe.org

2. Learning objectives
After this course you are able to:
• Understand what raster data is and how it can be used in
GIS

3. GIS Basics
2 common data models to
represent reality in a GIS:
• Vector
• Raster

4. Raster data
• Matrix of pixels or cells
• Rows
• Columns
• Resolution
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5. Raster data
• Resolution
• Data types:
• Integer – for discrete or
boolean (0,1) data
• Float – for continuous data
• NODATA, mv, nan
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pixel
height
width
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6. Raster resolution
High resolution Low resolution

7. Raster resolution
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8. What is Remote Sensing?RS in een notendop – Opbouw van RS afbeeldingen - Gebruik van False Coilour - Opdracht
MODIS

9. What is Remote Sensing?RS in een notendop – Opbouw van RS afbeeldingen - Gebruik van False Coilour - Opdracht
ASTER

10. RS in een notendop – Opbouw van RS afbeeldingen - Gebruik van False Coilour - OpdrachtWhat is Remote Sensing?
IKONOS

11. What is Remote Sensing?RS in een notendop – Opbouw van RS afbeeldingen - Gebruik van False Coilour - Opdracht
IKONOS

12. Aerial Photograph

13. Why raster data?
• Rasters can represent
continuous information
better than vectors, e.g.:
• Gradients in vegetation
cover
• Elevation
Can you name a few more?
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14. Raster types
• Discrete rasters: integer values representing classes
• E.g. Land-use map, soil map
• Continuous rasters: real values representing features
without sharp borders
• E.g. DEM, temperature map, soil moisture map, runoff map
• Boolean rasters: 1 or 0, representing true or false
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15. Single band rasters
Monochromatic image Gray scale image Color image
Colormap file

16. Consist of several single band rasters.
Each band relates to a range
in the electromagnetic
spectrum collected by a sensor.
Electromagnetic spectrum
Bands are commonly displayed as red
green and blue composits (RGB).
Multi-band rasters

17. Continuous raster data - examples
• Remote sensing data
• Digital Elevation Models
(DEMs)
• Interpolated point data
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18. Discrete raster data - examples
• Land-use map
• Source: CORINE 2000
• Soil map
• Source JRC
• Boolean maps
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19. Vector versus Raster
• Raster data is computationally less expensive to render than vector graphics
• Transparency and aliasing problems when overlaying raster data
• Vector data allows for visually smooth and easy implementation of overlay operations
• Vector data can be easier to register, scale, and re-project
• Vector data is more compatible with relational database environments, where they can
be part of a relational table as a normal column and processed using a multitude of
operators.
• Vector file sizes are usually smaller than raster data, which can be tens, hundreds or
more times larger than vector data
• Vector data is simpler to update and maintain, whereas a raster image will have to be
completely reproduced.
• Vector data allows much more analysis capability, especially for "networks" such as
roads, power, rail, telecommunications, etc.
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