Location on surface, portrayal, scale and more!!!!!

The Earth is not flat.

It is a sphere. This influences how we portray the Earth on two-dimensional (2-d) surfaces (i.e., maps) and how we define the location of points on the Earth’s surface (i.e., coordinate systems)

Scale

• Spatial scale describes the typical distance or area (horizontal or vertical) that a certain event occupies.

• The spatial scale of interest also influences how we portray the Earth and how we define a location on the Earth’s surface

For example, if one is interested in studying a phenomenon on ASU’s campus (a small SPATIAL scale), then a different map and coordinate system would be used than for a study of a global phenomenon (a large SPATIAL scale).

But what is a map and a coordinate system? Map = an abstraction of the Earth.

Most commonly, a 2-d representation of Earth’s surface.

Coordinate System= a method of defining points in a given space. In physical geography, coordinate systems allow us to uniquely define every point on Earth.

Cartography=the study of representing the spherical earth on a flat surface

Map Projection=a representation of Earth on a flat surface

Image from: http://www.kidsgeo.com/geography-for-kids/0030-map-projections.php

But what is a map and a coordinate system?

But what is a map and a coordinate system? Representing a spherical object on a

flat surface results in distortion There are many different map

projections which seek to accurately portray at least one of three main properties Shape (conformal projections) Distance (equidistant projections) Area (Equal area projections)

But what is a map and a coordinate system? There are three main classes of

projections Cylindrical Conic Planar

Image from: http://www.kidsgeo.com/geography-for-kids/0030-map-projections.php

But what is a map and a coordinate system? The standard line (or point) are the areas on

the globe in contact with the map surface (be it cylindrical, conical or planar) . Areas of the earth further from the standard line are more distorted.

The aspect refers to the location of the standard line (or point) Equatorial (standard line is the equator or latitudinal

line near the equator) Oblique (standard line is a mid latitude line) Polar (standard line is a polar latitude line

or the pole is the standard point)Image from: http://www.kidsgeo.com/geography-for-kids/0030-map-projections.php

But what is a map and a coordinate system? Therefore, map projections are often

named by their property, class, and aspect e.g., Conformal Conic Oblique

Famous projections have cooler names

Mercator = Conformal Equatorial Cylindrical (image from: geo.hunter.cuny.edu)

a. Also called "interrupted homolosine projection“

b. resembles a peeled orange 

c. land areas are shown with correct shape and size

 

d. Hard to use

Goode Projection: Best to show accurate shape & size of land

But what is a map and a coordinate system?

But what is a map and a coordinate system? Any location on earth can be uniquely defined by latitude

and longitude. This is called a Geographic Coordinate System

Latitude (or parallels): 90oS-90oN, 0o=equator. Longitude (or meridians):180oE-180oW, 0o= Prime

Meridian, 180oE=180oW=International Date Line

For example: A point given by 30oN and 90oW

The above image was obtained from: http://mcsd-sw.mcbarons.manheimcentral.org

But what is a map and a coordinate system?

The Township and Range system is often used as a coordinate system for smaller scales (e.g., the western United States)• 1 township is 36 square miles (6 miles on a side)• 1 section is 1 mile on a side (1 square mile) so 36 sections are

in 1 township

But what is a map and a coordinate system?

The Township and Range Grid is constructed using baselinesBaseline = reference line whose position is precisely known

Townships are measured from baselines (measure north-south) and range lines (measure east-west)Examples: the township north of baseline is T1N and the township east of rangeline is R1W

But what is a map and a coordinate system?

T2NR2W

But what is a map and a coordinate system?

T2NR2W

Another very common coordinate system for smaller scales is the Universal Transverse Mercator (UTM) coordinate system.

T2NR2W

There are 60 UTM zones, each covering about 6o longitude.

But what is a map and a coordinate system?

T2NR2W

Lets say I am interested in defining the locations of Tornadoes in the east-central US in the UTM system (i.e., UTM zone 16)

But what is a map and a coordinate system?

T2NR2W

The UTM zone 16 coordinates would be relative to a Transverse Mercator map projection with the standard line as a longitude through the east-central US. Distances, shapes, directions, and areas are reasonably accurate within the UTM zone 16.

But what is a map and a coordinate system?

Spatial Scale v Map Scale We have already defined spatial scale (e.g., the size of

an area/phenomenon) Map scale indicates what a distance on a map would be

on the earth’s surface Three main ways to represent map scale

Verbal: 1 inch on map=1,000 miles on surface of Earth Fractional: 1:24,000

E.g., 1 in (or mi or m) = 24,000 in (or mi or m) If the map scale is 1:100,000 and two points on a map

are 1 cm apart, then they are 1 km apart in reality (note: 1 km=100,000 cm)

Graphical:

Large Map Scale v Small Map Scale 1:10,000 is larger

scale than 1:1,000,000 because 1/10,000 is the bigger number. The 1:10,000 map would have more detail and represent a smaller area of the earth.

From: Svoma 2010

Spatial Scale v Map Scale

Larger Spatial Scale Smaller Spatial Scale

Larger Map ScaleSmaller Map Scale

Small scale maps depict large spatial scales.

Large scale maps depict small spatial scales.