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Introduction to GIS

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by

Rami Azzam

on 5 January 2014

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Transcript of Introduction to GIS

1- A location (or geospatial) component




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

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
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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.
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