Geographic Information Systems GIS Analysis and Modeling

1. Geographic Analysis Geographic questions: where, when, why, and how The purpose of the analysis is to answer questions about: - what existed at where, when, why, and how - what will happen at where in the future or in other locations

2. Organizing Geographic Data Data layers (shape file etc.) Feature types: points, lines, polygons Object types: geometric or thematic e.g. Development streets - line layer1 water - line layer2 parcels - polygon layer1 soils - polygon layer2

3. Overlay Arithmetic overlay Logic overlay Weighting input layers Raster vs. vector overlay

3.1 Arithmetic Overlay adding layers, subtracting, multiplication, division, etc. Raster Input data layer A Input data layer B Output data layer

3.1 Arithmetic Overlay .. Arithmetic operation on two data layers using the vector data model Attribute data Spatial data Input data layer A Input data layer B Output data layer

3.3 Weighting Input Layers Professional experiences Expert votes Empirical or analytical models

3.4 Raster vs. Vector Overlay - Every cell is executed, and the overlay result is a new layer Vector - The operation is executed only for areas of interest - New attribute items are created - New layers may be created that carry both the original and new attributes - The operation is generally more complex than raster overlay

Raster Overlay Vector Overlay http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

3.2 Logic Overlay Finding areas where certain conditions occur Boolean logic Mary Ruvane, UNC –Chapel Hill

Union INPUT COV UNION COV OUT INPUT COV UNION COV # # ATTRIBUTE # ATT # ATTRIBUTE # ATTRIBUTE 1 1 2 A 2 102 3 B 3 103 4 C 5 D OUT INPUT COV UNION COV # # ATTRIBUTE # ATT 1 1 1 2 1 2 102 3 2 A 1 4 2 A 2 102 5 3 B 2 102 6 3 B 1 7 2 A 3 103 8 3 B 3 103 9 4 C 3 103 10 5 D 3 103 11 4 C 1 12 4 C 2 102 13 5 D 2 102 14 5 D 1 15 1 2 102 Figure 4.2: Buffers around points, lines and a polygon In all cases the buffer polygons are shaded light grey while the input features are in black. http://hds.essex.ac.uk/g2gp/gis/sect44.asp

Intersect and Identity

Clip

Erase

Update

4. Proximity Analysis (Buffering) The identification of a zone of interest around an entity or a set of entities

Buffering http://www.sdsmt.edu/online-courses/geology/mprice/geo416/lecture9.ppt

Buffering A multi-distance buffer (each ring is 150 m) A single distance buffer (250 m) http://geology.wlu.edu/harbor/geol260/lecture_notes/notes_location1.html

5. Measurement Distances between points Nearest distances Functional distances Lengths of lines Perimeters and areas of polygons Centroid of an area Area of a profile Volume Shape Narrowest and broadest distances across a polygon Sinuosity of a line

5. Measurement .. Distances between Points - Euclidian distance

5. Measurement .. Nearest distances The Closest Facility

5. Measurement .. Functional Distance Three-minute response time from a fire station, City of Phoenix http://www.esri.com/mapmuseum/mapbook_gallery/volume17/public2.html

5. Measurement .. Lengths of lines Perimeters and areas of polygons

5. Measurement .. Centroid of an area It is used to represent a polygon by a single point Several methods to identify a centroid: mean value of vertices’ coordinates, center of the enclosing circle or rectangle, http://www.geoict.net/tgipage/Teaching/UNIT%207--PPT.pdf

5. Measurement .. Area of a profile Volume

5. Measurement .. Shape - how to measure shape of an area? - a compact shape has a small perimeter for a given area compare perimeter to the perimeter of a circle of the same area - shape = perimeter / area Narrowest and broadest distances across a polygon

5. Measurement .. Sinuosity of a line - the ratio of the actual length to the straight line length between point A and point B

Readings Chapter 5,6,9,10