GIS - - the best way to create ugly maps FAST

1. GIS - - the best way to create ugly maps FAST or GIS roots in Cartography

2. More bad maps…

3. Representing and Transforming • Graphic symbols • size, symbology, value, saturation, shape, arrangement, texture, focus • Classification procedures are used to ease user interpretation • Natural, quantile, equal interval, s.d. • Cartogram transformations distort area or distance for some specific reason More examples: US Transportation Survey

5. Georeferencing • Is essential in GIS, since all information must be linked to the Earth’s surface • The method of georeferencing must be: • Unique, linking information to exactly one location • Shared, so different users understand the meaning of a georeference • Persistent through time, so today’s georeferences are still meaningful tomorrow

6. Georeferences as Measurements • Some georeferences are metric • They define location using measures of distance from fixed places • E.g., distance from the Equator or from the Greenwich Meridian • Others are based on ordering • E.g. street addresses in most parts of the world order houses along streets • Others are only nominal • Placenames do not involve ordering or measuring

7. Placenames • The earliest form of georeferencing • And the most commonly used in everyday activities • Many names of geographic features are universally recognized • Others may be understood only by locals • Names work at many different scales • From continents to small villages and neighborhoods • Names may pass out of use in time

8. Postal Addresses and Postcodes • Every dwelling and office is a potential destination for mail • Dwellings and offices are arrayed along streets, and numbered accordingly • Streets have names that are unique within local areas • Local areas have names that are unique within larger regions • If these assumptions are true, then a postal address is a useful georeference

9. Where Do Postal Addresses Fail as Georeferences? • In rural areas • Urban-style addresses have been extended recently to many rural areas • For natural features • Lakes, mountains, and rivers cannot be located using postal addresses • When numbering on streets is not sequential • E.g. in Japan

10. Linear Referencing • A system for georeferencing positions on a road, street, rail, or river network • Combines the name of the link with an offset distance along the link from a fixed point, most often an intersection

11. Users of Linear Referencing • Transportation authorities • To keep track of pavement quality, signs, traffic conditions on roads • Police • To record the locations of accidents

12. Converting Georeferences • GIS applications often require conversion of projections and ellipsoids • These are standard functions in popular GIS packages • Street addresses must be converted to coordinates for mapping and analysis • Using geocoding functions • Placenames can be converted to coordinates using gazetteers

13. Latitude and Longitude • The most comprehensive and powerful method of georeferencing • Metric, standard, stable, unique • Uses a well-defined and fixed reference frame • Based on the Earth’s rotation and center of mass, and the Greenwich Meridian

14. Latitude and the Ellipsoid • Latitude (of the blue point) is the angle between a perpendicular to the surface and the plane of the Equator • WGS 84 • Radius of the Earth at the Equator 6378.137 km • Flattening 1 part in 298.257

15. Assign latitude to the y axis and longitude to the x axis A type of cylindrical projection Is neither conformal nor equal area As latitude increases, lines of longitude are much closer together on the Earth, but are the same distance apart on the projection Also known as the Plate Carrée or Cylindrical Equidistant Projection The “Unprojected” Projection

16. Map Projections A map projection is a set of rules for transforming features from the three-dimensional earth onto a two-dimensional display. No flat representation of the earth can be completely accurate, so many different projections have been developed, each suited to a particular purpose. Map projections differ in the way they handle four properties: Area, Angles, Distance and Direction. Rules: • No projection can preserve all four simultaneously, although some combinations can be preserved, such asArea and Direction • No projection can preserve both Areaand Angles, however. The map-maker must decide which property is most important and choose a projection based on that. Learn more: http://mac.usgs.gov/mac/isb/pubs/MapProjections/projections.html

17. Map Projection

18. Different Plane Locations and Viewpoints Normal or Polar Oblique Transverse orEquatorial

19. Different families of projections azimuthal conic cylindrical

20. Distortion patterns

21. conformal equal area direction distance Universal Transverse Mercator (UTM) • Projection properties • All Transverse properties • Standard line is a meridian • 60 zone divided • Projection uses • World Map

24. conformal equal area direction distance Robinson’sprojection Uses tabular coordinates rather than mathematical formulas to make the world "look right." Directions true along all parallels and along central meridian Distances constant along Equator and other parallels • Projection properties • Compromise • Projection uses • World atlas maps

25. State Plane Coordinates • Defined in the US by each state • Some states use multiple zones • Several different types of projections are used by the system • Provides less distortion than UTM • Preferred for applications needing very high accuracy, such as surveying

27. Mapping Lab

28. Geographic Data Models and GeoDatabases

29. 3 43 12 3 45 (v1,v2) 15 40 2 15 24 V 21 3 5 10 64 Geographic Data Models • Vector and Raster - two main families • Representation of geographic information: • Raster: location controlled, attribute measured • values are stored in ordered array, so that position in the array defines geographic location • Vector: attribute controlled, location measured • geographic coordinates are stored separately from attributes, connected with Identifiers

30. Rasters • How to represent phenomena conceived as fields or discrete objects? • Raster • Divide the world into square cells • Register the corners to the Earth • Represent discrete objects as collections of one or more cells • Represent fields by assigning attribute values to cells • More commonly used to represent fields than discrete objects • Characteristics: • Pixel size • The size of the cell or picture element, defining the level of spatial detail • All variation within pixels is lost • Assignment scheme • The value of a cell may be an average over the cell, or a total within the cell, or max, or min, or the commonest value in the cell, or presence/absence, or… • It may also be the value found at the cell’s central point, or systematic analigned

31. Legend Mixed conifer Douglas fir Oak savannah Grassland Raster representation. Each color represents a different value of a nominal-scale field denoting land cover class.

32. The mixed pixel problem

33. Methods of Grid Encoding • point-based • center point (regular grid) -DEMs, - but what if periodicity in landscape?; what if pop. density? • systematic unaligned (random in a cell) • area-based(have to integrate info...) • extreme value (max or min) • total (sum, like reflected light) • predominant type (most common) • presence/absence (binary result) • percent cover (% covered by single category) • precedence of types (highest ranking)

34. RASTERS… • Each cell can be owned by only one feature. • Rasters are easy to understand, easy to read and write, and easy to draw on the screen. A grid or raster maps directly onto an array. • Grids are poor at representing points, lines and areas, but good at surfaces. • Grids are a natural representation for scanned or remotely sensed data. • Grids suffer from the mixed pixel problem. • Grid compression techniques used in GIS are run-length encoding and quad trees.

35. Rasters and vectors can be flat files … if they are simple Flat File Vector-based line 4753456 623412 4753436 623424 4753462 623478 4753432 623482 4753405 623429 4753401 623508 4753462 623555 4753398 623634 Raster-based line Flat File 0000000000000000 0001100000100000 1010100001010000 1100100001010000 0000100010001000 0000100010000100 0001000100000010 0010000100000001 0111001000000001 0000111000000000 0000000000000000

36. 1 0 1 21 203 3 Compacting Raster • from simple matrix to... ...run-length encoding ...row differences encoding, TIFF ...Quadtrees, Morton numbers

37. Vector - Land Records Surveyed feature 20.37’ 26.23’ R 10’ 45.81’ 45.81’ 13 12 35.44’ 30.5’ 26.23’ GIS Link Survey / / / Survey point / 9 / / Computation

38. (x1,y1) (x2,y2) (x3,y3) (x5,y5) (x6,y6) (x4,y4) Vector Data Structure Alternatives 1 • Development trends: • increasing complexity, refining logic • making geographic relationships EXPLICIT • Spaghetti files (1974...) • the original CIA format • lines and points which the reader must organize • Polygon loops (location lists): • polygons stored as objects, polygonshading is easy, IF CORRECT! • problems: common line defined twice; slivers between adjacent polygons because boundaries not necessarily the same

39. 1 2 3 5 4 Vector Data Structure Alternatives 2 • Point dictionary • polygon descriptions refer to lists of fixedpoints with coordinates (point dictionaries) • similar to polygon loops, but instead of coordinates of vertices in polygon descriptions - IDs of vertices • Topological data structure • Organizes Points, Lines, and Areas as Nodes, Chains, and Polygons • The model: nodes bound chains, chains co-bound polygons;chains co-bound nodes, polygons co-bound chains... • the structure stores topological relationships between nodes, chains, and polygons; these relationships are used in defining chains through nodes, polygons through chains, etc. • Provides for contiguity, better quality control...

40. Topology • TOPOLOGY: study of basic spatial relationships based on intuitive notions of space (those not requiring numerical measurements); fundamental level of mathematics of space; • Topology IS NOT topography • TOPOGRAPHY: measurement/representation of earth elevation and related features (a form of general/ reference map) • Why topology in cartography/GIS • lines are coded once - avoids redundancy • data quality issue: [topo]-logical consistency

41. Basic arc topology n2 3 2 A 1 B n1 Topological Arcs File Arc From To PL PR n1x n1y n2x n2y 1 n1 n2 A B x y x y

42. II III B IV A I V C VI Tracking Topological Relationships • Connectivity • nodes bound chains • chains bound polygons in turn, • chains are bounded by nodes • polygons are bounded by chains U 1 2 3 4 Point table Node table ID Coord a <x,y> b <x,y> c <x,y> d <x,y> … <…> ID Chains 1 <list> 2 <list> 3 <list> 4 <list> Chain table ID Vertices From To Left Right I <list> 1 4 A U II <list> 1 2 U B III <list> 1 3 B A IV <list> 3 2 B C V <list> 4 3 A C VI <list> 2 4 U C Polygon table ID Chains A <list> B <list> C <list> U <list>

43. Typical Digitizing Situations overshoot, and what to do with it this is ideal, but... undershoot, and what to do

44. Planar Enforcement Is Not Enough • Interrelationships between semantic and spatial structures Each string is marked withleft and right labelsTrying to assemble polygonsfrom these strings: there maybe more than one label “to the left” of all strings forming a closed polygon… a standard topological error... However, these labels may be in container relationship in a domain map

45. 3 2 1 4 Automaticlabeling results…

46. Special Cases: 1 • B: basal nucleus of Meynert (C0004788) • LGP: lateral globus pallidus, C0262267 • Basal nucleus cells (B) are within LGP, but their precise locations not known  polygon is coded LGP, B is a secondary descriptor

47. SpecialCases: 3 • DG: dentate gyrus, C0152314 • PoDG: polymorph layer of the dentate gyrus • CA1: field CA1 of hippocampus (C0019564) • All of them have a common parent: hippocampus  a common parent is used to label polygon; polylines are labeled separately

48. Spatial Types – OGC Simple Features Composed Type SpatialReferenceSystem Geometry Relationship GeometryCollection Point Curve Surface Polygon MultiSurface MultiCurve MultiPoint LineString Line LinearRing MultiPolygon MultiLineString

49. Elements of a Geodatabase Geometric Network Feature Dataset Relationship Class Feature Class Annotation Class Object Class The Geodatabase Data Model

50. Feature Datasets • Container • Same spatial reference • Analogous to a coverage The Geodatabase Data Model