2- A graphic component

3- Can connect tabular data to map features

A picture or graphic located in reference to a known model of the earth.

Map

What is GIS

Representative Fraction (RF)

1:100,000 or 1/100,000

Statement Scale (Equivalence Scale)

“one millimeters to one million millimeters”

“one millimeter to one kilometer”

1" = 1 mile

Bar Scale

.

**Geographic Information System /**

United States

Geographical Information System /

Europe

Geomatique /

Canada

Georelational Information System /

Technology-based terminology

Natural Resources Information System

Spatial Information system

United States

Geographical Information System /

Europe

Geomatique /

Canada

Georelational Information System /

Technology-based terminology

Natural Resources Information System

Spatial Information system

**SYNONYMOUS TERMS**

Simplified Description

Map + Data

Has a map with a database behind it.

A system that:

Simplified Description

Provides a virtual representation of the real world and its infrastructure.

A system that:

Data

GIS = Geographic Information System

A system for:

spatial data

Components of GIS

Definition

capturing

managing

manipulating

displaying

analyzing

GIS Data

Latitude & longitude

X, Y components in a known geographic coordinate system

A street address

**Maps and Spatial Reference**

Maps are graphical representation of spatial data. They show locations of objects with attributes and their spatial distribution.

Two questions come to mind when trying to represent the earth or parts of its surface, on a map inside a GIS

Maps are reduction of the real world

How much reduction is needed?

**Map Scale**

Proportional to the level of detail

Low reduction : lots of detail

High reduction: limited details

**>**

**>**

Map Scale

1:1,000

1:12,500

1:100,000

Map Projection

A mathematical model that transforms the locations of features on the earth’s curved surface to locations on a 2-dimensional surface.

Projection

G

eographic

I

nformation

S

ystem

Map Projection Distortions

3D Earth

2D Map

Some distortions of area, shape, distance, and direction always result from this process. Shapes (angles), distances, directions and areal sizes cannot be preserved at once.

Shape

Area

Distance

Direction

Types of Projection

Conformal

(Preserves Shape)

Equivalent

(Preserves Area)

Compromise

(Preserves Neither)

Lambert Conformal Conic

Mercator

Albers Equal Area

Sinusoidal

Goodes Homolosine

Robinson

Sphere

SHAPE OF THE EARTH

Ellipsoid

Semi-Minor

Semi-Major

SHAPE OF THE EARTH

Major Ellipsoids

SHAPE OF THE EARTH

In reality, the shape of the Earth is highly irregular.

An ellipsoid-geoid model is commonly used to represent the shape of the Earth.

Ellipsoid is the reference surface for horizontal coordinates (lat/lon).

Geoid is the reference surface for elevation.

SHAPE OF THE EARTH - Geoid

A Geoid is the surface perpendicular to a plumb line, and for which the pull of gravity is a given value.

Surface on which the gravity potential is everywhere constant (equipotential).

Measured surface via instrumentation.

SHAPE OF THE EARTH - Datums

Ellipsoids model the shape of the earth but don’t tell where the center of the earth.

A frame of reference for measuring locations on the surface of the earth

"Measurements are referenced to a geodetic origin and an ellipsoid model".

A datum is a model that describes the position, direction and scale relationships of a reference surface to positions on the surface of the Earth.

Local datum

NAD27

Ellipsoid

CLARKE 1866

Earth-centered datum

NAD83

Ellipsoid

GRS80

Most Widely Used Local Datums

North American Datum

Clarke 1866

South American Datum

International

WGS Datum

Arc Datum

Clarke 1880

Tokyo Datum

Bessel

European

Datum

International

Coordinate Systems

Geographic coordinate system

Latitude and longitude are not uniform across the earth’s surface

Coordinate Systems

Geographic coordinate system

Coordinate Systems

Cartesian coordinate system

Measures of length and angle are uniform

+X

+Y

-X

+Y

-X

-Y

+X

-Y

Commonly used coordinate systems

Some standard coordinate systems used in the United States are:

Geographic Coordinates

Universal Transverse Mercator (UTM)

State Plane Coordinates (SPC)

Public Land Surveys (PLS)

To compare or edge-match maps in a GIS, both maps

MUST

be in the

same coordinate system

.

Many coordinate systems have default projections.

Coordinate Systems

Universal transverse mercator (UTM)

o

o

o

o

o

o

o

Coordinate Systems

Universal transverse mercator (UTM)

Uses Transverse Mercator projection (conformal)

Zones extend from 84 N to 80 S

Each zone: 6 longitude wide with a central meridian and zone origin

First zone: 180 W to 174 W

Second zone: 174 W to 168 W

doesn’t cover polar areas , why ?!

Coordinate Transformation

Coordinate Transformation

Need to unify into one coordinate system objects recorded in different coordinate systems.

Transformation is the derivation of one set of coordinates for a point whose coordinates are known in another coordinate systems.

o

o

**Introduction to GIS - The Earth Shape and Coordinate Systems**

Mapping is an abstraction process by which real world objects are measured, documented and stored. As a result of abstraction, the real world is both simplified and reduced in size.

What is the size of the earth and how is it related to the size of the map?

How can a spherical shape be represented by a flat map?

The scale of a map is the ratio or proportion between distances measured on the map and the corresponding distances measured on the ground.

An attempt to portray the surface of the earth or a portion of the earth on a flat surface.