Monday, May 12, 2008
Bolstad Chapter 11 Terrain Analysis
Terrain analysis is important in GIS because terrain dictates how water flows and where it collects, how much sunlight hits a place throughout the day/year, and what can be seen from where in different landscapes. DEMs provide important information about terrain: hillshade, slope, and aspect can be derived from this type of data. It's also possible to determine flow through and watershed boundaries for hydrologic functions with a DEM. When working with this raster data we can use 3D analyst or spatial analyst extensions.
Monday, April 21, 2008
Monday, April 14, 2008
Monday, April 7, 2008
Topics in Raster Analysis (Chapter 10 Bolstad)
Although most people work with vector-based data, raster-based data allows for different types of analysis which can be very cool; for example, site suitability analysis which might use DEMs and slope models are nicely suited for real-world visualization and modeling.
Reviewing....raster is a simple data structure made up of cells on a grid. Each cell has one value (ex- one elevation value per cell; if the resolution is 20' then the cell doesn't represent anything more detailed than those 20'). Raster uses much larger file sizes but it is a simpler file structure. The smaller the cell size, the higher the resolution which equals a bigger file!!!
Okay, on to the new stuff again: map algebra is a cell by cell combination of raster data layers. You can perform different functions on the data such as + - * / but that depends on which software you have. Problems can pop up relating to different cell sizes and overlapping, but you can 'resample' to achieve like size cells.
Other types analysis are local (using only 1 cell), neighborhood (cell with surrounding) and global (using the whole raster layer) to look at different raster layers. Local functions use the raster calculator for spatial analysis, and we can also reclassify (this is not worded correctly, i think) Reclassification simplifies data and it reminds me of 'dissolve'.
Reviewing....raster is a simple data structure made up of cells on a grid. Each cell has one value (ex- one elevation value per cell; if the resolution is 20' then the cell doesn't represent anything more detailed than those 20'). Raster uses much larger file sizes but it is a simpler file structure. The smaller the cell size, the higher the resolution which equals a bigger file!!!
Okay, on to the new stuff again: map algebra is a cell by cell combination of raster data layers. You can perform different functions on the data such as + - * / but that depends on which software you have. Problems can pop up relating to different cell sizes and overlapping, but you can 'resample' to achieve like size cells.
Other types analysis are local (using only 1 cell), neighborhood (cell with surrounding) and global (using the whole raster layer) to look at different raster layers. Local functions use the raster calculator for spatial analysis, and we can also reclassify (this is not worded correctly, i think) Reclassification simplifies data and it reminds me of 'dissolve'.
Chapter 9 Spatial Data Analyses
Spatial data analysis is related to geoprocessing and takes place with geoprocessing tools in ArcToolbox. Some of the functions are:
clip-
overlay-
amend/merge-
overlay options- where we get a lot of analysis in; combine spatial and attribute data
And now, a word about buffering: a buffer is an area drawn around a feature at a uniform distance. It usually represents an important area (maybe a floodplain, a protected species habitat, or a service area for a city). The features which lay inside the buffer have different status than the features which lay outside the buffer.
clip-
overlay-
amend/merge-
overlay options- where we get a lot of analysis in; combine spatial and attribute data
And now, a word about buffering: a buffer is an area drawn around a feature at a uniform distance. It usually represents an important area (maybe a floodplain, a protected species habitat, or a service area for a city). The features which lay inside the buffer have different status than the features which lay outside the buffer.
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