Geog. 377: Introduction to GIS - Lecture 18 Overheads 1 2. Measurement 3. Connectivity Topics Lecture 18: GIS Analytical Functionality (II) Readings on the topics Measurement: Chapter 6 Chrisman (2002): pp Connectivity: Chapter 7 in Aronoff (1993): pp Other readings Chapter 14 in Longley et al. (2005): pp

Geog. 377: Introduction to GIS - Lecture 18 Overheads 2 2. Measurement Operations: 2.1 Distance between features: Under Raster The spread function (Spread Function Figure)Spread Function Figure Under Vector 1) Point to point Straight line: Outlines Along a path: ∑di∑di∑di∑di

Geog. 377: Introduction to GIS - Lecture 18 Overheads Under Vector (continued…) 2) Point to Line To s To straight line: (Point to Straight Line)Point to Straight Line To polyline: (Point to Polyline)Point to Polyline 3) Point to Polygon (Point to Polygon)Point to Polygon 4) Line to Line (Line to Line)Line to Line 5) Line to Polygon (Line to line) 6) Polygon to Polygon (Line to line)

Geog. 377: Introduction to GIS - Lecture 18 Overheads 4 2. Measurement Operations: (continued …) 2.2 Lengths of linear features Under Raster Counting pixels Under Vector Sum of the lengths of line segments defining the linear feature 2.3 Perimeters of area features Under Raster Counting the number of exposed edges of exterior pixels (Figure)Figure Under Vector Sum of the lengths of line segments defining the boundary 2.4 Area of area features Under Raster Counting the number of pixels of the same label Under Vector The trapezoid approach (The Trapezoid approach)The Trapezoid approach

Geog. 377: Introduction to GIS - Lecture 18 Overheads 5 3. Connectivity Operations: 3.1 Connectivity measures Under Raster 4-connected (Diagram)Diagram 8-connected (Diagram)Diagram Under Vector Objects are identified under vector data model. connectivity can be determined based on physical connection 3.2 Proximity (buffering) Under Raster Calculating distance and thresholding (Raster Buffering)Raster Buffering The Nature of error with buffering under raster (Error)Error Under Vector Construct buffers for individual line segments and then resolve the overlaps (Vector Buffering)Vector Buffering

Geog. 377: Introduction to GIS - Lecture 18 Overheads 6 3. Connectivity Operations (Continued…) 3.3 Intervisibility operation (viewshed analysis) (Raster only, requires a DEM) Find out the area which can be seen from a point (viewshed)viewshed 3.4 Spatial Search The Point-In-Polygon Operation (Point-In-Polygon)Point-In-Polygon

Geog. 377: Introduction to GIS - Lecture 18 Overheads 7 Questions: 1. How to determine the size of a particular patch under the raster data model? (the size of one patch) 2. Buffering under raster is not accurate. Why people say that? What is a commission error and a omission error under the context of a raster buffer? 3. What is 4-connected and what is 8 connected? 4. How would one determine if a point is in a particular polygon or not? Why do people say that point-in-polygon is the fundamental operation for spatial search?