REVIEW LECTURE By Austin Troy

1. ------Using GIS-- Introduction to GIS REVIEW LECTURE By Austin Troy

2. Introduction to GIS I. What is GIS?

3. Introduction to GIS • WHAT IS GIS? Some definitions: • The complete sequence of components for acquiring, processing, storing and managing data (Star and Estes, 1990) • It is a configuration of computer hardware and software specifically designed for the acquisition, maintenance and use of cartographic data, (Tomlin, 1990) • It is a set of computer tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real for a particular set of purposes, (Borrough et al. 1998) • A system of hardware, software, data, people, organizations and institutional arrangements for collecting, storing, analyzing and disseminating information about areas of the earth. Source: adapted from UC Berkeley GIS Center

4. Introduction to GIS Limitations of GIS: • Simple geometry does not describe nature • Nature is impossible to quantify and measure accurately • When we represent nature on paper or on a computer we abstract and simplify • GIS is fundamentally an exercise in abstraction and approximation; • It is not like physics or math • It is complicated by scale • It is complicated by time

5. Introduction to GIS II. Data Structures

6. Introduction to GIS Entities and Fields • There are two general approaches for representing things in space: • Entities: objects, with precise location and dimensions and discrete boundaries (remember, points are abstractions). • Fields, or phenomena: a Cartesian coordinate system where values vary continuously and smoothly

7. Introduction to GIS Spatial data structures- Raster • Spatial features modeled with grids, or pixels • Cartesian grid whose cell size is constant • Grids identified by row and column number • Grid cells are usually square in shape • Area of each cell defines the resolution • Raster files store only one attribute, in the form of a “z” value, or grid code. • Consider the contrary….

8. Introduction to GIS Spatial data structures-Vector • Each point has a unique location • Points can create a line • Points and lines can scribe a polygon, whose angle points are given by “nodes” • Polygons are closed regions whose boundaries are made up of line segments connected at many angles. • Polygons generally define an area of homogenous phenomena • These phenomena can be described by one or more stored attributes

9. Introduction to GIS Spatial data structures-Vector • Vector files in ARC INFO are topologically encoded. These are true vector files. • that is, each point, line and node is defined in relation to every other point, line and node • Polygon and line topology is encoded using arcs • Arcs are vertices and nodes connected by lines • Topology allows for powerful analysis tools

10. Introduction to GIS Importance of Topology • The computer needs topology to be able to address many types of spatial problems • With topology, data is stored very efficiently, allowing spatial data sets to be processed quickly • Topology facilitates analyses, such as: • modeling flow through networks • combining adjacent polygons with similar traits • determining distances between and among objects • surface modeling

11. Introduction to GIS Spaghetti Data Model Just because feature looks like a point, line or polygon does not mean it’s topological Spaghetti Model is: Non-topological data model that looks like vector collections of line segments and points with no real connection or topology Only stores features coordinates; there are no relative relationships encoded in this model each feature has no knowledge of other features that it intersects, is adjacent to, contiguous with or near

12. ------Using GIS-- Introduction to GIS TIN: Triangulated Irregular Network What is a TIN? Alternative model for representing terrain (from lecture 16) A TIN is a data structure that defines geographic space as a set of contiguous, non-overlapping triangles, which vary in size and angular proportion. Like grids, TINs are used to represent elevation surfaces, and can be created directly from files of elevation sample points, but with TINs these sample points are irregularly distributed.

13. ------Using GIS-- Introduction to GIS Three Dimensional data — TIN Note the triangular facets defined by points

14. ------Using GIS-- Introduction to GIS TINs • TIN triangles vary in size with the complexity of the terrain; • How are the sample points that define the triangles determined? • Several algorithms exist for choosing significant sample points from a DEM to make a TIN: • Very Important Points method (VIP) • Maximum z tolerance method

15. ------Using GIS-- Introduction to GIS TINs • Maximim z tolerance: like VIP, an offset is determined, but this uses a specified maximum z-tolerance to decide which points are selected. The z-tolerance is selected through an iterative process. First it constructs a candidate TIN, and for each triangle in the TIN it calculates the elevation difference of the grid cells bounded by it. If the cell with the largest difference to triangle is greater than the z tolerance, that point is flagged for addition to the TIN model. This is what AV asks you for when you make a TIN

16. Introduction to GIS III. Database Models

17. Introduction to GIS • Three Classic Database Models • Hierarchical • Network • Relational -Arc View and Arc Info use this model

18. Introduction to GIS Data Types An individual data point, or datum (singular of data), can be of any number of types, including: • number (must be continuous); below are subclasses: • Currency (has specific decimal behaviors) • Byte (0 to 255) • Date • Integer • Long (integers, with a greater range) • Single precision (with decimals) • Double precision (like single, with a greater range) • string (text: numbers can be represented as text, but they have no numerical properties) • Boolean (yes, no) • Object (holds data objects)

19. Introduction to GIS Hierarchical Database Model A one-to-many method for storing data in a database that looks like a family tree with one root and a number of branches or subdivisions. Problem: linkages in the tables must be known before Groovy 70s TV Action shows Drama Sitcoms Three’s company Love Boat Dukes of Hazzard Dallas Fantasy Island CHIPs Gavin McLeod Larry Hagman John Ritter Tom Wopat Eric Estrada Larry Wilcox Ricardo Montalban Suzanne Somers

20. Introduction to GIS Networked Database Model A database design for storing information by linking all records that are related with a list of “pointers.” Problem: linkages in the tables must be known before. Not adaptable to change. Action shows Drama Sitcoms Three’s company Love Boat Dukes of Hazzard Dallas Fantasy Island CHIPs NBC CBS ABC

21. Introduction to GIS Network and Hierarchical Examples • Think about file storage in MS Windows—analogous to a hierarchical database • Shortcuts turn this into the equivalent of a network database

22. Introduction to GIS Relational (Tabular) Database Model • A design used in database systems in which relationships are created between one or more flat files or tables based on the idea • that each pair of tables has a field in common, or “key”. In a relational database, the records are generally different in each table • The advantages: each table can be prepared and maintained separately, tables can remain separate until a query requires connecting, or relating them, relationships can be one to one, one to many or many to one

23. Introduction to GIS Data Tables (flat files) Records are the unit that the data are specific to Fields, or columns, are attribute categories Cells are where individual values of a record for a field are stored fields Headings: are the labels for the columns records cells

24. Introduction to GIS Data key Is a field that is common to two or more flat files; allows a query to be done across multiple tables or allows two tables to be joined Flat file: professor info Flat file: course info

25. Introduction to GIS • Relational database: one to many relationship One-to-many relationship In this case, several people co-own the same lot, so no longer one lot, one person

26. Introduction to GIS Assuming each owner owned several parcels, we would structure the database differently One-to-many relationship Note: this table includes data pertinent only to Flores’ ownership of these properties

27. Introduction to GIS IV. Queries

28. Introduction to GIS Queries in Arc View • Arc View queries only select (highlight) records • When a record is selected, so is its corresponding feature • To summarize selected values, must use the “statistics” function or “summarize” button • To create new values based on a query, must use the “calculate” tool.

29. Introduction to GIS • So what can Arc View do with queries? • A query selects records; once selected you can: • Look at the selection • Requery the selection • Do stats on the selection • Create new fields that recategorize the selection by an an attribute field • Create new fields by doing calculations across several fields • Create a shapefile from the selection

30. Introduction to GIS • Reclassing: say we wanted to prioritize inner city areas for urban redevelopment projects: • Let’s query based on unemployment and home value • Based on these we’ll make High, Medium and Low priority areas; everything else is not classified • Tracts with median home value < $100,000 and un-employment > 12% are “High”

31. Introduction to GIS

32. Introduction to GIS Multi-layer queries Let’s say we want to select all the houses in our sample database that overlay fire hazard zones and then run some statistics

33. Introduction to GIS Now with “sample houses” active, we click select by theme and tell it to choose features that intersect the features of fire hazard zone

34. Introduction to GIS Those that overlay a hazard zone are selected

35. Introduction to GIS Now we can run statistics on the selection This tells us that 2011 houses overlay fire zones Since we ran stats on the Price field, it also tells us that the mean price for these properties is $460,127!

36. Introduction to GIS Now, say we want to select features from layer A that are within a distance of features in layer B

37. Introduction to GIS V. Legend editing

38. Introduction to GIS Legend Editor Review: there are two ways to classify your legend: • Graduated color: number data type • Unique value: primarily for string data (categories) Class. method Class. field

39. Introduction to GIS Legend Editor Often categories must be aggregated and redefined: this land use map had over 110 categories that were condensed to 30

40. Introduction to GIS Legend Editor To do this I had to type in what code ranges corresponded with my land use designations (e.g. Single family residential, commercial) and assign each a color. I decided on the classes The colors had to be chosen strategically so that important classes stood out and so that similar classes (e.g. SF and MF residential)were in the same color family

41. Introduction to GIS Legend Editor With graduated color (numeric) legends, we must decide: • How many classes • By what method will the data be broken up • Natural breaks, quantile, equal area, standard deviation • The default is natural breaks

42. Introduction to GIS Legend Editor Here we have houses graduated by sales price. We have accepted arc view’s default of 5 classes and natural breaks.

43. Introduction to GIS Legend Editor Notice how it changes when we classify by equal interval—most are in the lowest category now because outliers make the intervals meaningless

44. Introduction to GIS Legend Editor Another way to display point data is by the graduated symbol method—the larger the value, the larger the symbol

45. Introduction to GIS VI. Vector geoprocessing

46. Introduction to GIS Using the Geoprocessing Wizard • The GP wizard allows you to dissolve, clip, merge, intersect, union and spatial join

47. Introduction to GIS Spatial Join • Assigns data from one location in one layer to same location in another • Can assign polygon data to a point that overlays • Can assign point to point and point to line distances between two layers • Simple adds attributes to the DBF table

48. Introduction to GIS Buffering: A GIS Classic • Arc View 3.2 allows for buffer operations • Allows for variable width based on attribute • Allow multiple buffers

49. Introduction to GIS VII. Vector representation

50. Introduction to GIS Vector Representation:Points Simple points Nodes: topological junction between line features Vertices: define “kinks” All zero dimensional: points don’t exist in reality