Chapter 3 Employment of Projections and Thematic Base-Map

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```					Chapter 3 Employment of Projections and
Thematic Base-Map Compilation
Definition: Tangent or secant to equator is termed regular, or
normal.
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
Shape.
• 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
projection
• All parallels are
concentric
• 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-
Latitudes
• 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
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
Exercise
• 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
elements
– 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
Census
Data
Metropolitan/
Micropolitan
Remotely Sensed Data
• Landsat (flying altitude, cycle, scenes/day)
• SPOT
• NETSAT
www.census.gov
1. Click Your Gateway to Census 2000
2. Under American FactFinder, click “Enter
a street address to find Census 2000 data”
4. Select a Geography (such as Census
Tract) and Click “Map It”
5. Or click “Go”
GIS Census Data
http://arcdata.esri.com/data/tiger2000/tig
•   Select TN
•   Under “Select by County” – choose
“Putnam”
•   Under “Available data layers” – select
– “Census Tract 2000”
– “County 2000”
•   Under “Available Statewide Layers”
select
– Census Tract Demographics (PL94)
•   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.
to the current project: tgr47141cty00.shp,
tgr47141lkA.shp, tgr47141demtrt00.shp.
-- Continued --
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
problem.
current project.
• Join tgr47000demtrt.dbf to layer
“tgr47141trt00”
– Right-click on the “tgr47141trt00”
and choose “Joins and
Relates/Joins”
– Join is based on “STFID” from this
layer and “tgr47000demtrt”
– Click “Advanced” and select the
second options “Keep only
matching records”. Clikc OK to
continue.
Homework 4 – 1
due : 10-19-2005 midnight

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.