Thematic Mapping Techniques Yang Shao University of North Carolina at Chapel Hill

Outline Cartogram Concept Type Challenges Flow map 3-D phenomena Internet Map/GIS Applications

Most commonly used method of thematic mapping Choropleth mapping Proportional symbol mapping Dot density mapping Thematic Mapping Techniques

Additional thematic mapping techniques Cartograms Flow maps Mapping 3-D phenomena

Cartograms Instead of normalizing data within polygons: We can change the polygons themselves! Maps that do this are known as cartograms Cartograms distort the size and shape of polygons to portray sizes proportional to some quantity other than physical area

Conventional Map of 2004 Election Results by State Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan

Electoral College Cartogram of 2004 Election Results by State Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan

Conventional Map of 2004 Election Results by County Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan

Population Cartogram of 2004 Election Results by County Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan

Three types of cartograms Non-contiguous Contiguous Dorling cartograms

California

Challenges of cartogram mapping Recognition the displayed data the original geographical model Shape Orientation Contiguity No commercial software available

Flow Map From B.D. Dent, Cartography (1996)

Mapping 3-D phenomena

3D Applications (selected examples) Digital urban Geological/geophysical exploration 3D processes such as ocean currents or lava flows

Two kinds of volumetric phenomena 2.5-D phenomena have a single z value for each x and y location. True 3-D phenomena have multiple z values for each X and Y location.

Challenges in 3-D mapping Data source Land cover Houses – location, height, shape, size Roads DEM The limitations of software

Approach: integrated use of multiple data sources 1. 2D ground plans 2. Z value from remote sensing? Light Detection and Ranging (LIDAR) High spatial-resolution image 3. Use local height data to extrude the building footprints detailed on high-resolution map

(Norbert Haala, Claus Brenner and Karl-Heinrich Anders)

Building height and high spatial-resolution image

x y Y = tan(α) × x α

Algorithm design: Identify shadow (shadow vs. water) Measure shadow size, orientation, and shape Calculate building height

Shadow vs. water

3-D urban (example)

Software considerations Create your own 3D symbols –Building –Vegetation –people 2.5-D vs. 3D

Internet Map/GIS Applications 1. Location Services 2. Routing and Direction services 1 and 2 are often combined together. Examples are: - recently become a part of Microsoft Target of these services – general public for their daily life. 3. Public notification – government can publish their spatial data using Internet map services.

Internet Map/GIS Applications(Cont.) Example – Nuclear Waste Shipment Routes Map on Internet 4. Database query – Many public agencies are opening their databases to the public. The city of Ontario, CA, has set up an application that allows people to query the city’s parcel tax database for a specific owner or tax ID number and get a map of the parcel along with a detailed tax history of that subject. You can find similar examples in many counties and cities’ websites.

Nuclear Waste Transportation Routes

Examples of Internet Mapping Applications Location Services (1)Static Internet Maps – no interaction Examples: Campus Map, Location maps for hotels,. Only permanent map is needed. Stored as GIF or JPEG images. UNC Campus Map (GIF format): Red Roof Chapel Hill Location (GIF Format):

Examples of Internet Mapping Applications (Cont.) Web Server HTML pages with GIF or JPEG image Web Users Web Users Structure of Static Map Service Software Requirement: HTML Editors. Anyone who can edit a html document can create a static map service. Sometime Javescript/Vbscript may be required to handle the update (like weather maps – they are static for a certain period.)

Examples of Internet Mapping Applications (Cont.) (2) Interactive Location Service As previously mentioned, mapquest, mapblast, google earth, virtual earth, and yahoo map service, etc, all provide interactive location service on Internet. These services generally target people who want to locate a place by an address (similar to geo-coding in ArcView.) or a place name. Many Internet users are using them. Users can also customize a map and print them out. Features of these services: -Customizable -Usually maps can be displayed in multiple pre-defined scales -Format of maps: JPG, GIF, etc., all compressed raster formats. -Maps can downloaded and printed, but only in a very limited size (no more than 740*800 for mapblast) -Also provide routing/directional service

Examples of Internet Mapping Applications (Cont.) Data Server Web Server Web Users Web Users Sending Request Wrapping images in HTML and sending back HTML to users Request data from serverCompiling data and converting them into compressed images Typical Structure of Interactive Location Service

Google Earth VS Virtual Earth Google Earth combines satellite imagery, maps and other popular geographic data. Internet users could use it to explore interested places, plan a trip, create 3D maps, etc. Provides directions, interactive maps, and satellite/aerial imagery of the United States. Can also search by keyword such as type of business.