Gis functions

GIS FUNCTIONS
Institute of Geology University of AJ&K, Muzaffarabad

• Homes
• School Districts
• Streets
• Zip Codes
• Cities
• Counties
CAPTURE
GIS FUNCTIONS
STORE
QUERY
ANALYZE
DISPLAY
OUTPUT
GIS FUNCTIONS

• Capturing Data: A GIS must provide methods for inputting
geographic (coordinate) or tabular (attribute) data. The
more input methods available, the more versatile the GIS.
• Storing Data: There are two basic data models for
geographic data storage: vector and raster. A GIS should
be able to store geographic data in both models.
• Querying data: A GIS must provide utilities for
finding specific features based on location or
attribute value.
• Analyzing data: A GIS must be able to answer
questions regarding the interaction of spatial
relationships between multiple data sets.
• Displaying Data: A GIS must have tools for
visualizing geographic features using a variety of
symbology.
• Output: A GIS must be able to display results in a
variety of formats, such as maps, reports, and
graphs.

Other features of a GIS
• Produce good cartographic products
(translation = maps)
• Generate and maintain metadata
• Use and share geoprocessing models
• Managing data in a geodatabase
using data models for each sector

The geovisualization view
• A GIS is a set of intelligent maps and other views
that show features and feature relationships on the
earth’s surface.
• Various map views of the underlying geographic
information can be constructed and used as
“windows into the geographic database” to support
query, analysis, and editing of geographic
information.
• Each GIS has a series of two-dimensional (2D) and
three-dimensional (3D) map applications that
provide rich tools for working with geographic
information through these views.

The geodata view
A GIS is a spatial database containing
datasets that represent geographic
information in terms of a general GIS
data model— features, rasters,
attributes, topologies, networks, and so
forth.
"Data is the rocket fuel of GIS, the
elixir of life for a box of tools. "

The geoprocessing view
• A GIS is a set of information transformation tools
that derive new information from existing datasets.
• These geoprocessing functions take information from
existing datasets, apply analytic functions, and write
results into new derived datasets.
• Geoprocessing involves the ability to program your
work and to automate workflows by assembling an
ordered sequence of operations.

GIS maps
• GIS maps bring the world to your
computer screen. In this lesson
you learn how features in the
real world are represented on
GIS maps, how they are
organized into layers, and how
they are displayed at different
scales.

How is a GIS Map Organized?
• A GIS map consists of one or
more data frames
• A data frame contains a
collection of thematic layers.
• Layers, in turn, contain a
collection of features that
represent real-world objects.

• On a GIS map, features have a
location, shape, and a symbol.
• Features grouped into a layer
have the same shape and
characteristics and are located
within the same geographic
extent.
• To make a GIS map, you can add
as many layers as you want.

• These four layers might
be used by a city
government to create a
GIS map.
• The layers all contain
features located within
the city's boundaries,
but each one represents
a distinct "theme."
• The layers are drawn on
top of each other to
create an informative
GIS map.

Representing the Real World
• In the real world, geographic
objects have a wide variety of
shapes.
• In a GIS map, geographic objects
are primarily represented as
point, line, and polygon features.

Representing the Real World
• In this map of South America
– Countries are represented as
polygons
– Rivers are represented as lines
– Cities are points
• Each feature shape has its
own unique set of
characteristics.
– The geometry type used to
represent an object depends
on the amount of detail that
needs to be shown
– The same object may be
represented as a polygon in
one layer and a point in
another layer.

Points
• Composed of one coordinate pair
representing a specific location
on the earth's surface.
• Used for objects too small to be
polygons, such as cities, trees,
and hospitals.

Lines
• A sequence of two or more
coordinate pairs.
• Has length, while polygons have
two intrinsic values, perimeter
and area.
• Represent objects too narrow to
be polygons, such as streets,
rivers, and telephone lines.

Polygons
• Composed of one or more lines whose
starting and ending coordinate pairs
are the same.
• Have two intrinsic values
– Perimeter
– Area
• Represent objects large enough to have
boundaries, such as
– Countries
– Building footprints
– Lakes

What is a feature?
• A feature represent the real
world-object on a map
• A feature has four components
1. Shape
2. Location
3. Symbol
4. Attributes

• A shape of the feature can be
point, line and polygon
• A city can be represented as a
point
• A river can be represented as a
line
• A country can be represented as
a polygon

• A feature has location and can be
represented as latitude and
longitude
• A feature has a symbol, color,
outline and pattern or all of these
• A feature has attributes:
• Attributes are information that
describe the features

Linking Features to
Information
• On a GIS map, there's more to a
feature than its location and shape.
– There's all the information associated
with that feature.
• For a road, this might include its
name, speed limit, and whether it's
one-way or two-way.
• For a city, this might include its
population, demographic
characteristics, number of schools,
and average monthly temperatures.

Linking Features to
Information
• A particular type, or category, of
information associated with a feature in a
GIS is called an attribute.
– For example, population can be an attribute of
a city, country, continent, and other features.
• Feature attributes are stored in an
attribute table.
• In an attribute table, each feature is a
record (row) and each attribute is a
column, or field.
• The attributes for all the features in a
layer are stored in the same attribute
table.

Linking Features to
Information
• This attribute table
for a layer of cities
stores each
feature's
 ID number
 Shape
 Name
 Country in which it's
located
 Status

Linking Feature to Information
• A feature on a GIS map is linked
to its record in the attribute table
by a unique numerical identifier
(ID).
• Every feature in a layer has an
identifier.

• Because features on the map are
linked to their records in the
table
 you can click a feature on the map
and see the attributes stored for it
in the table.
• When you select a record in the
table, the linked feature on the
map is automatically selected as
well.

• In this map of
India, the city of
Bombay is
selected.
• Its record is also
selected in the
attribute table.
• The unique
identifier for
Bombay is stored
in the FID field.

• Links between features and
attributes make it possible to ask
questions about the information
stored in an attribute table and
display the answer on the map.
• This linkage makes GIS maps
much more informative than
static maps.

What is a layer?
• A layer is a collection of features
• Features in a layer represent the
same theme, such as mountain,
peak, road or lakes.
• Features in layers have same
shape and same set of attributes
• The ability to organize
information about real world
features into layers and view
layer together on a map

• On paper map scale is fixed you
can not change it. Features are
always the same size
• On GIS map scale is dynamic.
You can zoom in and out to
change the scale and see the
features with more or less detail

What is scale?
• Scale is the relationship between
the size of the feature on a map
and its actual size in the real
world
• Scale can be expressed as a ratio
such as 1:10,000
• This scale means that a feature
on a map is 10,000 times smaller
than it corresponding feature in
the real world

Understanding Map Scale
• Scale is the relationship between the size
of features on a map and the size of the
corresponding objects in the real world.
• Scale is commonly expressed as a ratio, or
representative fraction, such as 1:24,000.
• This scale means one unit on the map is
equal to 24,000 units on the earth.
• Another way of thinking about it is that
the objects on the earth are 24,000 times
larger than the features on the map which
represent them.

• You will commonly see references
to two types of maps:
– Large-scale
• Covers a small area in more detail
• i.e. a map of city streets or a building plan
– Small-scale
• Covers a large area in less detail
• i.e a world map,.
• GIS maps are dynamic—you can
change the scale to see more or
less detail as desired.

• Map on the left
– Large scale
– A small area of the
earth's surface (the
city of San Diego,
California)
– Features such as
roads are visible.
• Map on the right
– Small scale
– Bigger area of the
earth's surface (the
continental U.S.)
– But with less detail

All over the world,
organizations are using GIS to
– Manage the environment
– Work more efficiently
– Provide better customer service
– Save money

Gis functions

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