chapter 3 employment of projections and thematic base-map compilation definition: tangent or secant...

Chapter 3 Employment of Projections and Thematic Base-Map CompilationDefinition: 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 4Spring 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– Adjacent maps fit well.

Other Projections• Gall-Peters Projection - Cylindrical, equal-area

rectangular projection with standard parallels at 45o.• 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”

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

http://arcdata.esri.com/data/tiger2000/tiger_download.cfm

• Select TN• Under “Select by County” – choose

“Putnam”• Under “Available data layers” – select

– “Census Tract 2000”– “County 2000”– “Line Features -Roads”

• Under “Available Statewide Layers” select

– Census Tract Demographics (PL94)• Click “Proceed to Download”• Click “Download File” once the file is

ready.• 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 problem.

Add and Join Data• Add tgr47000demtrt.dbf to your

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 – 1due : 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