Synthesis of GIS Section

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Unformatted text preview: Synthesis
of
GIS
Section
 
 Here
are
the
main
points
that
the
students
should
understand
from
our
just
 completed
GEOG170
section
on
Geographic
Information
Systems.
 • • • • GIS
(a
Geographic
Information
System)
is
a
computer
system
capable
of
 capturing,
storing,
querying,
analyzing
and
displaying
geospatial
data.
 GIS
requires
a
computer,
GIS
software
and
data.
 We
use
GIS
because
“almost
everything
happens
somewhere”
and
a
GIS
lets
 us
analyze
that.
 Many
industries
use
GIS,
including:

banking,
retail,
insurance,
media,
real
 estate,
defense,
education,
civil
engineering,
economic
development,
 elections,
public
works,
urban
planning,
public
health,
mapping,
agriculture,
 environmental
management,
public
safety,
transportation
and
utilities.
 Geospatial
problems
can
be:
 o Local
or
global
 o Practical
or
exploratory
 o Have
time
scales
which
are
 Operational:
happen
in
real
time
(like
emergency
dispatch)
 Tactical:
have
a
medium
term
impact
(what
do
we
do
next
 hour/week/year)
 Strategic:
where
do
we
want
to
go
in
the
long
term
 Many
disciplines
go
into
designing
a
GIS,
including
cartography,
cognitive
 science
(human/machine
interactions),
computer
science,
law,
statistics,
etc.
 We
need
to
make
sure
that
our
computerized
portrayal
of
the
world
is
true
to
 the
“real
world”
 GIS
data
is
both
spatially
referenced
(we
know
where
it
is
on
the
earth)
and
 contains
attributes
(what
we
know
about
that
place)
 There
are
two
types
of
views:
 o Discrete:
well
defined
boundaries
of
features
or
phenomena
 o Continuous:

we
have
a
value
for
every
location
in
a
grid
 Attributes
can
be
partitioned
as:
 o Nominal:

the
type
of
feature
has
a
name,
like
that
of
a
road
 o Ordinal:
the
attribute
has
a
ranked
order,
like
a
percentage
 o Interval:

the
attribute
falls
within
a
range
of
values
(i.e.
70‐80%
forest
 cover)
 o Ratio:
so
many
per
unit
area
or
population
(i.e.
incidents
of
crime
per
 100,000
population,
or
number
of
trees
per
acre)
 o Count
how
many
things
are
present
(i.e.
population
in
a
given
 polygon)
 GIS
data
is
represented
as
points,
lines
(arcs),
or
area
(polygons)
 A
surface
is
a
special
type
of
point
data
which
provides
a
value
for
every
cell
 in
a
grid
 • • • • • • • • • • • • • • • • • • • • • • • • • Data
may
be
represented
as
a
raster
(a
value
for
every
grid
cell)
or
a
vector
 (data
is
only
shown
for
those
features
of
interest
(i.e.
the
boundaries
of
a
 county)
 Database
is
a
structured
collection
of
data
that
can
be
queried
 Some
types
of
digital
GIS
data:
 o DRG
(Digital
Raster
Graphic)
is
a
raster/scan/picture
of
a
1:24,000
 USGS
topographic
map
 o DLG
(Digital
Line
Graph)
is
a
vector
representation
of
the
same
thing
 o DOQ
(Digital
Orthophoto
Quadrangle)
is
an
orthophoto
which
 corresponds
to
the
spatial
extent
of
a
1:24,000
quadrangle
 The
U.S.
government
provides
a
wide
range
of
digital
data
for
free
 Metadata
is
data
about
data

and
provides
information
including
the
spatial
 resolution,
quality,
and
technical
specifications
for
the
data
 A
relational
database
relates
two
or
more
databases/layers/coverage’s
(note
 the
ambiguity
in
terminology)
based
upon
a
common
field
 Know
the
difference
between
fields
and
records
in
a
database
 Set
operations
are
used
to
manipulate
databases
 o Union
 o Intersection
 o Difference
 o Join
 Boolean
(T/F)
operations
are
used
to
query
databases
(=,
<,
<=,
>,
>=)
 AND,
OR
and
NOT
can
be
used
to
join
Boolean
operations
 o AND
means
both
statements
are
true
 o OR
means
either
statement
is
true
 o NOT
means
the
second
statement
not
true
 A
common
computer
language
for
executing
Boolean
statements
is
SQL
 (Structured
Query
Language)
 The
syntax
of
SQL
is
“Select
<attributes>
from
<relation>
where
<condition>
 o Attributes
are
fields
in
a
database
 o Relation
is
the
name
of
a
database
 o Condition
is
a
Boolean
statement
 Know
Dr.
John
Snow’s
Cholera
map
of
1854
 Investigation
techniques
 o Induction
starts
with
the
data
 o Deduction
starts
with
the
theory
 o Normative
starts
with
the
condition
you
want
to
optimize
for
 Modeling
is
dynamic
 Spatial
analysis
is
static
 Methods
for
investigation
include
 o Queries
 o Measurements
 Pythagorean
(statutory
miles),
or
 Great
Circle

(nautical
miles)
which
account
for
curvature
of
 the
earth
 o Transformations
 • • • • • • • • o Data
descriptions
(i.e.
stats)
 o Optimization
(i.e.
best
route)
 o Hypothesis
testing

(true
or
not)
 Compactness
of
shape
is
a
measure
used
for
Congressional
redistricting
 Common
transformations
are
buffering,
overlays
and
reclassification
 Operations
can
be
 o Polygon
on
polygon
 o Point
in
polygon
 o Line
in
polygon
 Overlays
can
be
a

 o Clip
 o Intersection
 o Union
 Reclassification
is
used
to
re‐assign
values
to
a
single
attribute
or
range
of
 attributes
 o Often
used
to
simplify
data
 Descriptive
statistics
help
explore
data
 o Common
are
mode,
median,
mean
and
standard
deviation
(average
 deviation
from
the
mean)
 Visual
tools
like
the
histogram
can
be
used
to
visually
display
stats
 Discuss
spatial
autocorrelation
 ...
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This note was uploaded on 02/23/2011 for the course GEOL 170 taught by Professor Staff during the Spring '11 term at Maryland.

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