Download GIS and Spatial Analysis: Line Data Analysis in Geog473, Spring 2009 - Prof. Kuan Song and more Exams Geography in PDF only on Docsity! Geog473, Spring 2009 Kuan Song, Department of Geography, UMD -1- Spring 2009 Geog 473: GIS and Spatial Analysis Line Data Analysis Kuan Song Department of Geography University of Maryland March 30, 2009 • New approaches on the class: – Mock exam 1 week before the final – 1 Bonus question every lecture for students outside Geography – Students who answered bonus questions correctly need to register their names after the lecture – Lab/homework structure unchanged – Everyone who gave suggestions in response to my last email gets 2 bonus points on top of midterm – In the future, valid suggestions also receive bonus points on top of the final Lecture outline 1. Linear geographic objects and GIS line features 2. Length and fractal dimension 3. Line density 4. Line direction and orientation 1. Representing linear objects in GIS 1.1 Linear geographic object • A geographic object that can be represented by a line or a set of lines. • Examples: rivers, roads, electric and telecommunication networks. 1.2 Line feature in GIS • A map feature that has length but not area at a given scale. (ESRI GIS Dictionary) • Polyline, arc, chain Yukon Ohio M is si ss ip pi Arkansas Gila Red Sna ke Missouri Colville Rio Grande P ecos Koyu kuk Kus kokw im St. Cla ir G re en North Platte Columbia Al ab am a C ol o r a d o Niagara Illi no is Susitina Klama th P ee D ee Kings C on ne ct ic ut 1.3 Scale and representation Depending on the scale, geographic objects can be represented as different GIS data types: line or polygon POTOMAC RIVER Clopper Lake Monocacy River Potomac River Potomac The Potomac River is represented as line or polygon in GIS Geog473, Spring 2009 Kuan Song, Department of Geography, UMD -2- 2. The length of a line feature in GIS n i idL 1 di is the Euclidean distance of segment i. (x1, y1) (x2, y2) (xa, ya) (xb, yb) X Y 2.1 Calculating line length: the sum of the segments d1 d2 d3 The length: • Question: How to calculate Euclidean Distances? In 2-d and 3-d • Hint: triangle with a right angle X Y 2.2 Scale and length The lengths of linear objects are dependent on the scale of measurement. Po tom ac Question: What is the length of the Potomac River? Benoît B. Mandelbrot, 1924- . Emeritus at Yale University. Best known as the "father of fractal geometry". How long is the coast of Britain? Statistical self-similarity and fractional dimension. Science: 156, 636-638. 1967 2.3 Fractal dimension of a linear geographic object A measure of how "complicated" the object is. 200km 100km 50km • The coastline length of Britain 1.81.734506950 1.42.0280028100 1.12.3236011.8200 Log(N)Log(L)Total lengthNumber of segments (N)Scale (L) )21 21 21 21 log()log( )log()log( )/log( )/log( LL NN LL NN D The fractal dimension of a linear object: Unit: km N1, N2: number of segments L1, L2: the length (scale) of yardstick. • 1≤D≤2. • A higher D value indicates a more complicated linear object. • When D=2, the line “turns into” an area.
