GIS Lecture Notes - Raster Analysis
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These notes provide an overview of raster analysis techniques, focusing on zonal and global functions within GIS. They discuss the categories of raster functions, highlighting the differences between local, focal, zonal, and global approaches. The document also covers basic operations like zonal statistics and global functions, and concludes with key takeaways for effective GIS application.
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Raster Analysis: Zonal and Global Functions Categories of Raster Functions 1. Local Functions: New cell values depend on the same cell in one or more input layers. 2. Focal Functions: New cell values depend on neighboring cells. 3. Zonal Functions: Operate on groups of cells (zon...
Raster Analysis: Zonal and Global Functions Categories of Raster Functions 1. Local Functions: New cell values depend on the same cell in one or more input layers. 2. Focal Functions: New cell values depend on neighboring cells. 3. Zonal Functions: Operate on groups of cells (zones) treated as single units. 4. Global Functions: Treat the entire raster as one unit of analysis. Zonal Functions Definition of Zones: ○ Homogeneous areas based on specific attributes. ○ Zones can be contiguous (connected) or non-contiguous (separate). Basic Operations: ○ Parceling: Identifies zones by assigning unique values to clusters of cells with similar attributes. Achieved through reclassification or converting polygons to rasters. Example: Assigning unique values to lakes in a raster. ○ Area & Perimeter Calculations: Summing cell dimensions based on spatial resolution. Less accurate for irregular shapes unless zones align with raster orientation. Zonal Statistics: ○ Calculations like mean, maximum, or standard deviation for each zone. ○ Examples include calculating land cover area or analyzing specific attribute values. Global Functions Apply to the entire raster as a single unit. Examples of global operations: ○ Global Statistics: Mean, maximum, or standard deviation for the entire dataset. ○ Found in the Source tab in software like ArcGIS. Map Algebra Combines local, focal, zonal, and global operations for complex analyses. Performed using tools like the raster calculator in ArcGIS. ○ Example: Combine focal statistics from one layer with local operations on another. Key Takeaways Understand the distinctions between local, focal, zonal, and global functions. Recognize that zonal and global operations, while fewer, are crucial for real-world applications and often serve as inputs to other analyses. Mastery of these concepts is essential for effectively leveraging tools like ArcGIS in unscripted scenarios.
