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

• 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

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

•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 http://www-personal.umich.edu/~mejn/election/

Electoral College Cartogram of 2004 Election Results by State
Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan http://www-personal.umich.edu/~mejn/election/

Conventional Map of 2004
Election Results by County
Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan http://www-personal.umich.edu/~mejn/election/

Population Cartogram of 2004
Election Results by County
Michael Gastner, Cosma Shalizi, and Mark Newman- University of Michigan http://www-personal.umich.edu/~mejn/election/

•
Non-contiguous
•
Contiguous
•
Dorling cartograms

California

http://www.ncgia.ucsb.edu/projects/Cartogram_Central/

http://www.ncgia.ucsb.edu/projects/Cartogram_Central/

http://www.ncgia.ucsb.edu/projects/Cartogram_Central/

• Recognition the displayed data the original geographical model
Shape
Orientation
Contiguity
• No commercial software available

From B.D. Dent, Cartography (1996)

http://www.esri.com/software/arcgis/extensions/3danalyst/

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.

• 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

y x
α
Y = tan(α) × x

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

Shadow vs. water

3-D urban (example)

3-D urban (example)

• 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: www.mapblast.com
- recently become a part of Microsoft www.mapquest.com
www.yahoo.com/map
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 http://www.state.nv.us/nucwaste/states/us.htm
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): http://www.unc.edu/courses/2001fall/engl/011/058/Pictures/campus_map.htm
Red Roof Chapel Hill Location (GIF Format): http://www.redroof.com/reservations/inn_details.asp?innNumber=201&HD=yes

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.)
Request data from server
Data Server
Compiling data and converting them into compressed images
Web Server Wrapping images in
HTML and sending back
HTML to users
Web
Users
Sending
Request
Wrapping images in HTML and sending back
HTML to users
Web
Users
Typical Structure of Interactive Location Service

• 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.
http://earth.google.com/products.html
http://maps.google.com/
• Provides directions, interactive maps, and satellite/aerial imagery of the United States. Can also search by keyword such as type of business.
http://local.live.com/