Intro to GIS
What is GIS ?
• A computer system for
- collecting,
- storing,
- manipulating,
- analyzing,
- displaying, and
- querying
geographically related
information.
Google Earth is an online GIS system
History of GIS
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1963-1977 innovation
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1981-1999
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Canadian land inventory system, Harvard
Graphics & S.A. Lab, US Census Bureau
ArcInfo, GPS, MapInfo, TIGER, NSDI,
MapQuest
2000-present exploitation
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>$7 billion industry, >1 million users
Demand for GIS professionals
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In the US in 2005
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500k using GIS as part of job; growing at
15% each year
Job market demand 75k/year
50k US students/year take a GIS class
4000 certified graduates/year
Source: ESRI
An example of GIS: composite of layers
In general GIS cover 3
components
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Computer system
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Hardware
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Computer, plotter, printer, digitizer
Software and appropriate procedures
Spatially referenced or geographic
data
People to carry out various
management and analysis tasks
Geographic Data
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Geospatial data tells
you where it is and
attribute data tells
you what it is.
Metadata describes
both geospatial and
attribute data.
In GIS, we call geographic data as GIS data or spatial data
1. Geospatial data
Traditional method
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To represent the geographic data is
paper-based maps
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Geology map
Topographic map
City street map (we still use it a lot)
...
GIS: a simplified view of the real
world
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Discrete features
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Points
Lines
Areas
Networks
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A series of interconnecting
lines
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Continuous features
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Road network
River network
Sewage network
Surfaces
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Elevation surface
Temperature surface
Points
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A point is a 0 dimensional object and
has only the property of location (x,y)
Points can be used to Model features
such as a well, building, power, pole,
sample location ect.
Other name for a point are vertex,
node
Point
Lines
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A line is a one-dimensional object
that has the property of length
Lines can be used to represent road,
streams, faults, dikes, maker beds,
boundary, contacts etc.
Lines are also called an edge, link,
chain, arc
In an ArcInfo coverage an arc starts
with a node, has zero or more
vertices, and ends with a node
Line
Areas (Polygons)
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A polygon is a two-dimensional object
with properties of area and perimeter
A polygon can represent a city, geologic
formation, dike, lake, river, ect.
Other name for polygons face, zone
Area
Topology needed
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A collection of numeric data which clearly describes
adjacency, containment (coincidence), and
connectivity between map features and which can
be stored and manipulated by a computer.
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A set of rules on how objects relate to each other
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Major difference in file formats
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Higher level objects have special topology rules
Two basic data models to
represent these features
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Raster spatial data model
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Define space as an array of equally sized cells arranged in rows and
columns. Each cell contains an attribute value and location
coordinates
Individual cells as building blocks for creating images of point, line,
area, network and surface
Continuous raster
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Discrete raster
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Numeric values range smoothly from one location to another, for
example, DEM, temperature, remote sensing images, etc.
Relative few possible values to repeat themselves in adjacent cells, for
example, land use, soil types, etc.
Vector spatial data model
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Use x-, y- coordinates to represent point, line, area, network,
surface
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Point as a single coordinate pair, line and polygon as ordered lists of
vertices, while attributes are associated with each features
Usually are discrete features
DIGITAL SPATIAL DATA
• RASTER
• VECTOR
• Real World
Source: Defense Mapping School
National Imagery and Mapping Agency
Raster and Vector Data Models
Real World
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10
G
B
G G
B
B
BG G
B G G
B G
BK
BG
B B
B
B
Raster Representation
600
Trees
500
400
Y-AXIS
300
Trees
House
200
River
100
100 200
300 400 500
X-AXIS
600
Vector Representation
Source: Defense Mapping School
National Imagery and Mapping Agency
Example: Discrete raster
Example: continuous raster
Xie et al. 2005
Raster
Real world
Vector
Heywood et al. 2006
Effects of changing resolution
Heywood et al. 2006
Vector – Advantages and
Disadvantages
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Advantages
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Good representation of reality
Compact data structure
Topology can be described in a network
Accurate graphics
Disadvantages
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Complex data structures
Simulation may be difficult
Some spatial analysis is difficult or impossible to
perform
Raster – Advantages and
Disadvantages
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Advantages
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Simple data structure
Easy overlay
Various kinds of spatial analysis
Uniform size and shape
Cheaper technology
Disadvantages
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Large amount of data
Less “pretty”
Projection transformation is difficult
Different scales between layers can be a nightmare
May lose information due to generalization
Grid Properties
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Each Grid Cell holds one
value even if it is empty.
A cell can hold an index
standing for an attribute.
Cell resolution is given as its
size on the ground.
Point and Lines move to the
center of the cell.
Minimum line width is one
cell.
Rasters are easy to read
and write, and easy to draw
on the screen.
2. Attribute data
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Attribute data is about “what” of a
spatial data and is a list or table of data
arranged as rows and columns
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Rows are records (map features)
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Each row represents a map feature, which has
a unique label ID or object ID
Columns are fields (characteristics)
Intersection of a column and a row shows
the values of attributes, such as color,
ownership, magnitude, classification,…
examples
3. metadata
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Meta is defined as a change or transformation. Data is
described as the factual information used as a basis for
reasoning. Put these two definitions together and
metadata would literally mean "factual information used as
a basis for reasoning which describes a change or
transformation."
In GIS, Metadata is data about the data. It consists of
information that describes spatial data and is used to
provide documentation for data products. Metadata is the
who, what, when, where, why, and how about every
facet of the spatial data.
According to the Federal Geographic Data Committee
(FGDC), metadata is data about the content, quality,
condition, and other characteristics of data.
Why use and create metadata
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To help organize and maintain an organization's spatial
data
- Employees may come and go but metadata can
catalogue the changes and updates made to each spatial
data set and how each employee implemented them
To provide information to other organizations and
clearinghouses to facilitate data sharing and transfer
- It makes sense to share existing data sets rather
than producing new ones if they are already available
To document the history of a spatial data set
- Metadata documents what changes have been made
to each data set, such as changes in geographic projection,
adding or deleting attributes, editing line intersections, or
changing file formats. All of these could have an effect on
data quality.
Metadata Should Include Data
about
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Date of data collected.
Date of coverage generated.
Bounding coordinates.
Processing steps.
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Software used
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RMSE, etc.
From where original data came.
Who did processing.
Projection
coordinate System
Datum
Units
Spatial scale
Attribute definitions
Who to contact for more information
See an example of non-standard metadata (see)
Federal Geographic Data Committee’s
(FGDC) Content Standard for Digital
Geospatial Metadata (CSDGM)
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The FGDC is developing the National Spatial Data
Infrastructure (NSDI) in cooperation with organizations
from State, local and tribal governments, the academic
community, and the private sector. The NSDI
encompasses policies, standards, and procedures for
organizations to cooperatively produce and
share geographic data.
The objectives of the CSDGM are to provide a common
set of terminology and definitions for the documentation
of digital geospatial data.
CSDGM (FGDC-STD-001-1998)
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Metadata =
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Identification_Information
Data_Quality_Information
Spatial_Data_Organization_Information
Spatial_Reference_Information
Entity_and_Attribute_Information
Distribution_Information
Metadata_Reference_Information
Connect to http://www.fgdc.gov/metadata/csdgm/
4. Geodatabase
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Before geodatabase, in one GIS project, many
GIS files (spatial data and nonspatial data) are
stored separated. So for a large GIS project, the
GIS files could be hundreds.
Within a geodatabase, all GIS files (spatial data
and nonspatial data) in a project can be stored
in one geodatabase, using the relational
database management system (RDMS)
Types of geodatabases
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personal
enterprise
Personal Geodatabase
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The personal geodatabase
is given a name of
filename.mdb that is
browsable and editable by
the ArcGIS, and it can also
be opened with Microsoft
Access. It can be read by
multiple people at the same
time, but edited by only
one person at a time.
maximum size is 2 GB.
Multiuser Geodatabase
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Multiuser (ArcSDE or enterprise) geodatabase
are stored in IBM DB2, Informix, Oracle, or
Microsoft SQL Server.
It can be edited through ArcSDE by many users
at the same time, is suitable for large
workgroups and enterprise GIS
implementations. no limit of size. support raster
data.