j.b. krygier: geography 353: lecture outline

Geography 353 Cartography and Visualization

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Geog 353 Lecture Outline: Geographic Framework
Update: 17/8/19

Making Maps book: Chapter 5: Geographic Framework

much of the information on this page was condensed, consistently illustrated, and made much better for the 5th chapter in Making Maps.
use this page for additional reference.

Introduction

Geographic Framework

I. Flatten the earth's curved surface: Map Projection

II. Zoom in: Map Scale

III. Locate: Map Coordinates

I. Introduction to Map Projections and Map Design

Map Projection: peel and flatten the earth...like an orange peel

Map projections are an important aspect of all mapping as all maps require the transformation of the surface of the spherical earth to a flat surface

This transformation always introduces some kind of distortion

distortion of area, shape, angles, etc.

We are used to seeing the world distorted: it looks natural

The goal is to select a map projection whose distortion does not interfere with the purpose of any given map.

infinite number of map projections
selection of appropriate base map projection driven by map content

Projections are important to mapping and GIS:

use them to focus reader's attention
amplify and provide selective detail for map's message
most important: poorly chosen map projections can distort your thematic data

Vital Map Projection Issues:

What are the basic characteristics of the map projection process?
What are the basic kinds of map projections and distortions?
Choosing Appropriate Map Projections

Cool Free Map Projection Software (Download): G.Projector

2. What are the basic characteristics of the map projection process?

how does map projection work?

The geographic grid or graticule

Locations on the sphere: latitude and longitude (one of many coordinate systems)

But globes are not that useful for most mapping tasks...so flatten the earth:

earth: geoid

reference ellipsoid: geodesy

called nominal, reference, or generating globe

Map projection: transformation of the spherical surface into a plane surface

All meridians and parallels are transformed in this process: the graticule
All human and physical earth features (coasts, rivers, lakes, boundaries, etc.) are also transformed in this process

3. What are the basic kinds of map projections and distortions?

Mark Monmonier in How to Lie with Maps: map projection is a "white lie"

Map projection process always results in some kind of distortion

distortions of areas, shapes, distances, and directions
something must always give: cannot preserve all of these together
Making Maps PDF) Ch 5. Distorting Data
Important: projections matter because of what they do to mapped data

Tissot's Indidicatrix: perfect circles of equal size on the globe; reveal patterns of distortion on projected maps.

Example: Mercator Projection:

Example: Equal Area Rectangular Projection:

Importance of scale and map projection

large scale mapping: distortion less noticeable; important if digital (GIS)
small scale mapping: fundamentally important

three basic kinds (categories, families) of map projections
five major kinds (categories) of map projections

3a Three Basic Kinds (Families) of Map Projections

Based on the idea of developable surfaces: attribute of the map projection process: what kind of flattenable surface are you projecting the sphere onto?

light source of the projection inside globe
shadow cast on plane, cylinder, cone
corresponds to azimuthal, cylindrical, and conic projection families
gives you very different looking maps with different distortions
Tangent and Secant Cases with distortions (dark = more distortion)

Azimuthal Family:

plane

tangent at a point on the sphere (simple form): standard point
or pass through the sphere (secant form): standard line

Tangency can be varied: varies the projection

polar aspect: tangency at a pole
oblique aspect: tangency at mid-latitude
equatorial aspect: tangency at equator

Distortions increase from standard point or line

increase outward in concentric bands
conformal azimuthal projections: area exaggeration increases outward
equal area azimuthal projections: shape distortion increases outward
can be varied to preserve area, angle, distance, or direction

Cylindrical Family:

cylinder

tangent at one or more lines: standard line(s)
equator is most common standard line

Tangency can be varied

Distortions increase away from the line(s) or tangency

Conic Family:

cone

tangent along one or more standard lines

Distortions increase away from the line(s) of tangency

Second major aspect of map projections

Review five major kinds (categories) of map projections based on the characteristics they preserve from the spherical earth (what they don't distort)

3b. Map Projections and what they Preserve from the Spherical Earth

Preserving Area: Equal Area or Equivalent Projections

area relationships are preserved
linear or distance distortion occurs as a consequence, skewing shape

Peters Equal-Area Map Projection: you give up shape to preserve area

Equal area projections very important to thematic mapping as much of thematic mapping consists of mapping area data

Equal area projections are a good general default for all thematic maps:

Lab Project!
US States: conic equal area projections are optimal

Map Projections in ArcGIS

1) Start ArcMap

2) Add, to your data frame a base map Countries.lyr (in ESRIDATA_2000/world folders)

make sure the layer is visible.

3) Add a lat/long graticule as another layer

from the ESRIDATA_2000/world folders add latlong.shp

Remember: equal area (equivalent) is best default: so change projection

4) Right mouse click on the data frame your layers are in, and select Properties.

select the Coordinate System tab.
select Predefined then Projected Coordinate Systems
ArcGIS gives you some categories to choose from: we have a world map, so select the World folder to see a few dozen map projections appropriate for world maps.
select the Robinson and hit ok

5) Check out the characteristics of the Robinson in ArcGIS's desktop help.

It preserves neither shape or area! But it looks ok.

While the equal area map projections are the best default

several other options for special cases

Preserving Shape: Conformal Projections

Mercator map projection is conformal (and cylindrical)

Angular relationships are preserved from points, and shape is preserved for small areas around a given point

Can never preserve areas (Equal Area) and shape (Conformality) at the same time

Useful for navigation, and mapping phenomena with circular radiation patterns

Preserving Distance: Equidistance Projections

Equidistance map projection is equidistant (and conic)

Distance is correct from one to all other points, or from a few points to others, but not from all points to all other points

Cannot preserve distances (Equidistance) and preserve area (Equal Area)

Preserving Direction: Azimuthal Projections

Azimuthal map projection preserves direction (and is azimuthal)

Preservation of direction from one central point to all other points

Can occur on equal area, conformal, and equidistant projections

Compromise Projections

Robinson map projection: preserves nothing, but looks good (and is cylindrical)

a compromise which attempts to preserve enough of area, shape, distance, and direction so that the earth "looks right"

was used by National Geographic on their World Maps

4. Choosing Appropriate Map Projections

Basic guidelines and projections appropriate for particular circumstances
Given the purpose and goal of your map, consider...

Projection properties:

Which projection family: azimuthal, cylindrical, conic?
- often more of an aesthetic choice
Which properties need to be preserved given the purpose of the map?
- vital! not aesthetic!
- equivalency (areas)
- conformality (shape)
- equidistance (distance)
- azimuthality (direction)
ArcMap:
- Help: Map Projections
- or projection name: Mercator, Albers...etc.

Map Projection Center:

center the projection given the purpose of the map?
Key: when setting up a base map: select a standard point or line near the center of your area of interest to minimize distortion
Recentering map projections: center the map projection on the area of interest
Recentering in ArcMap:

1) return to the properties of your dataframe and the Coordinate System tab
2) the Robinson projection you chose should be hi-lighted in the window: hit the Modify button
- in the Central_Meridian row type -84 (84 degrees W. of Greenwich, 0 degrees) then OK
3) The world should recenter on the meridian running through Delaware Ohio.
- try this with a map of the US
Your Project: you will adjust the center of the projection so that your state/s does not look tipped

Familiarity and Aesthetics

Will the projection be familiar enough to users so as not to detract from the purpose of the map?
is it appropriate to "surprise" the user with an unfamiliar projection to communicate something?

Suggestions for Mapping the World

equivalency (areas preserved) is fundamentally important
ArcGIS) Mollweide
ArcGIS) Robinson
ArcGIS) Peters (nope!)

Suggestions for Mapping Continents and Large Countries

Projections suitable for world maps are usually not suitable for mapping continents.

ArcGIS) Lambert equal area azimuthal projection

...and for the United States...

ArcGIS) Albers equal area
Lab: this is best!

Suggestions for Creative Solutions to the Employment of Projections

1. Using interrupted map projections

Schjerning map projection: interrupted

Goodes map projection: interrupted over oceans (top) versus land (bottom)

Fuller map projection: cut and assemble globe

2. Using hemispheric map projections: the view from space

Orthographic map projection: like lookin' at a globe

Orthographic map projection: used for locator insets

Erwin Raisz oblique map projection: just cool

3. Enlarging the center of the map

Various odd map projections: focus attention on area of interest

4. Showing rings of activity

The "Ring of Fire": Eckert versus Azimuthal Equidistant map projections

In all these cases you have to understand what is being distorted

Don't select a projection on its "look" alone

The UPS Map Projection: something wrong?

For Football Fans: about as amusing as map projections get

"The map projection provides the geometrical framework for all the points, lines, and areas compiled on the final map. Projection is a key element in the overall design. It controls the locational accuracy and final appearance of the mapped area and can be used to provide a focus for the map's message." (Borden Dent)

II. Map Scale

Making Maps PDF) Ch 5. Map Scale

III. Map Coordinates

Making Maps PDF) Ch 5. Map Coordinates

Conclusions

Lab project: setting up your state map in ArcGIS/ArcMap

You will have to choose the map projection of your state map

E-mail: jbkrygier@owu.edu

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