Chapter 3 Employment of Projections and Thematic Base-Map

Document Sample
Chapter 3 Employment of Projections and Thematic Base-Map Powered By Docstoc
					Chapter 3 Employment of Projections and
Thematic Base-Map Compilation
Definition: Tangent or secant to equator is termed regular, or
Tangent or secant to a meridian is the transverse aspect.
Tangent or secant to another point on the globe is called oblique.

Chapter 4. Census Data

                          Weeek 4
                         Spring 2007
         Choosing Projection
• First step: determine Location,Size and
• Rules (to reduce distortion):
  – Tropical areas : use cyclindrical projectionn
    (true at equator)
  – Temperate areas: use conical projection (true
    only at parallel between equator and poles)
  – Polar areas: use azimuthal projection (true only
    at center point)
                 World Projection - 1
• Equal-area projections are good
  choices. Shape distortion, especially
  along the peripheries of the map.
    – Mollweide projection: equator is a
      standard line, equally divided. Central
      meridian is ½ of the equator and drawn
      perpendicular to it. Parallels length not
      true to scale(except 40o40’). Max
      distortion at the extremes, where the
      intersections of the meridians and
      parallels are the most oblique.

    – Hammer projection: curved parallels,
      reducing distortion at extremes.
      Identical outlines as in Mollweide.
      More difficult than Mollweide to
      construct due to curved parallels.
          World Projection

• Boggs eumorphic projection – the poles on the Boggs
  are emphasized by the converging meridians. A
  combination of sinusoidal (Sanson-Flamstead) and the
  Mollweide. Better shape preservation along the equator.
   Continental Mapping – good choices include
   Bonne, Lambert azimuthal, Albers equal-area and sinusoidal.
• Bonne Projection –
  equal-area conical
• All parallels are
• Commonly used for Asia,
  NAmerica, SAmerica,
  Australia and others
• Shape distortion at the NE
  and NW corners
• Selection of central
  meridian is crucial.
  Large and Small Countries at Mid-
• Bonne, Lambert azimuthal equal-area or the Albers equal-area
  may be suitable.
• Lambert equal-area azimuthal projections – if point of tangency is
  the equator and some meridian, it is referred as Lambert equal-area
  meridional projection. If tangency is between equator and pole, than it
  is called “oblque” case” (fig 3.4)
• Albers equal-area projection – conic with two standard parallels,
  good for E-W extent, desirable properties
    –   Equal-area projection
    –   Max-scale eroor is app. 1.25% over an area the size of the US
    –   Straight lines for meridians and right angles to parallels
    –   Parallels are concentric circles – easy constructed
    –   A single-cone projection properties do not deteriorate in an E-W direction
    –   Adjacent maps fit well.
                Other Projections
• Gall-Peters Projection - Cylindrical, equal-area
  rectangular projection with standard parallels at 45 o.
• Figure 3.8
• Selection of State Projection – must be equal-area.
  State Plane Coordinate System adopts three
  conformal projections
   –   Lambert conformal conic for states in E-W dimensions
   –   Transverse Mercator for states with N-S dimensions
   –   Oblique Mercator or portions of Alaska
   –   Transverse is developed by rotating the normal aspect of
       the Mercator where the cylinder is tangent to the equator to
       a position where it is tangent to a meridian, they are tangent
       to two meridians
• Find the projections used in State Planes for
  Tennessee, North/South Pennsylvania..
Geographic Units, Data Sources
                           Geography Defined
• Absolute / Relative locations
• Cartogram (fig 4.2)
• Geographic Research
    –   Areal or Spatial Association: florist shops in relation to high-rise office building
    –   Forms and Processes: process results in patterns
    –   Spatial Interaction: road network and traffic
    –   Distance Decay: decreasing occurrence from center point.
• Concepts in Geography
    – Direction
    – Distance
    – Scale
    – Location
    – Distribution: patterns, dispersion
    – Localization: spatial clustering
    – Functional Association: occurrence of objects as a response to the presence of other
    – Spatial Interaction – diffusion
    – The Regional Concept – a region is an internal homogeneity set it apart from others.
    – Concept of Change.
           Spatial Dimensions
• Forms:
  –   Points
  –   Line
  –   Area
  –   Volume
  –   Space-Time
• Discrete/Sequential/Continuous Phenomena
  – Discrete : integer numbers
  – Lines, cases make a sequential phenomena
  – Continuous: no gap between values, weight, time.
 Measurement Scales (Table 4.3)
• Nominal Scaling
   – Grouping, 0/1,A/B/C.. For identification purpose
• Ordinal Scaling
   – Ranking, but ratio is not proportional
• Interval Scaling
   – Numerical scores, no origin, any beginning point may
     be used. Fahrenheit temperature, relative ranking
• Ratio Scaling
   – With known starting point, such as Kelvin temperature,
     elevation, weight
       Remotely Sensed Data
• Landsat (flying altitude, cycle, scenes/day)

1. Click Your Gateway to Census 2000
2. Under American FactFinder, click “Enter
   a street address to find Census 2000 data”
3. Enter your home address, then press GO
4. Select a Geography (such as Census
   Tract) and Click “Map It”
5. Or click “Go”
                          GIS Census Data
•   Downloaded from
•   Select TN
•   Under “Select by County” – choose
•   Under “Available data layers” – select
     – “Census Tract 2000”
     – “County 2000”
     – “Line Features -Roads”
•   Under “Available Statewide Layers”
     – Census Tract Demographics (PL94)
•   Click “Proceed to Download”
•   Click “Download File” once the file is
•   You will have to view the PL 94-171
    Quick Reference Guide link to find out
    the field name and field description for
    the demographic data.
        - Continued -
• You will get 4 zip files plus one readme.html.
• Unzip these four files (in fact, they are 3
  shapefiles and 1 demographic data). Make
  sure you put them in same folder (you’d
  better create a data folder under your current
  working folder)
• Start “ArcMap” from “Start”
• Once the program started, you will be
  prompted to begin your program with “A
  new empty map” or other two options. Click
  OK to continue.
• Click “Add Data” to add the following layers
  to the current project: tgr47141cty00.shp,
  tgr47141lkA.shp, tgr47141demtrt00.shp.
             -- Continued --
• Add “Structure” and “Addresses” to your
  current project.
• You might find the projection causing
  problem on one of the layer. If so, then
  defining the projection will take care of the
 Add and Join Data
• Add tgr47000demtrt.dbf to your
  current project.
• Join tgr47000demtrt.dbf to layer
   – Right-click on the “tgr47141trt00”
     and choose “Joins and
   – Join is based on “STFID” from this
     layer and “tgr47000demtrt”
   – Click “Advanced” and select the
     second options “Keep only
     matching records”. Clikc OK to
                Homework 4 – 1
               due : 10-19-2005 midnight

• Download your county data (2000 County, Block Group
  2000, Demographics (SF1), Line Features - Roads)
• Join Table from tgr47000sf1grp.dbf to your county’s block
  group by “Stfid” (see instruction on the link)
• Plot your county based on the population (field name
  POP2000) using 3 classes.
• Save your project as HW4-yourname.mxd under your
  homework folder.
• Send email to me with link to your homework mxd