A Review

1
A Review

• True or False Correct or Incorrect
• The world is a sphere .
• Latitude lines are parallel
• Longitude Lines are parallel
• A conic projection shows the entire earth
• An azimuthal projection shows accurate direction
• Stateplane projections are designed to show local
  areas
• Universal Transverse Mercator is a form of grid
• East of Longitude 0 and North of Latitude zero
  has all negative coordinates

2

• NAD83 is less accurate than NAD27
• Stateplane coordinates correspond across state
  borders
• UTM coordinates are impacted by political
  boundaries.
• Which is the longest line Zero Longitude, 90
  degrees Latitude, Zero degrees Latitude

3

• The impact on the accuracy of maps increases as
  scale increases
• Large scale maps show large areas
• Small scale maps show large areas
• 120000 is a smaller scale than 12,000,000
• Which of these scale represents a large scale
  local area 12,000,000 120000 12400

4

• Locational accuracy increases as scale
  increases or decreases
• Crime mapping usually occurs at a small or
  large scale?
• Geometrically the simplest GIS feature is a
• Nodes represent the middle or any location on a
  line

5
Building complex features

• Simple geographic features can be used to build
  more complex ones.
• Areas are made up of lines which are made up of
  points represented by their coordinates.
• Areas Lines Points

6
Areas are lines are points are coordinates
7
Properties of Features

• size
• distribution
• pattern
• contiguity
• neighborhood
• shape
• scale
• orientation.

8
Basic properties of geographic features
9
GIS Analysis

• Much of GIS analysis and description consists of
  investigating the properties of geographic
  features and determining the relationships
  between them.

10
Arc/Node Topology
11
(No Transcript)
12
The base concept is the Cartesian coordinate
system
13
Arcs begin and end with nodes
14
Polygons are defined by the arcs
15
Contiguity is maintained through defining the
polygons on each side of an arc or lineWhat do
we have to know about the arc?
16
Networks are defined through arc/node topology
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
Simple rules ...

• All arcs begin and end with nodes
• Turns in the middle of arcs are called vertices
• Curved lines have many vertices
• Dangling nodes in polygon coverages often
  represent errors
• Network coverages often have dangling nodes

21
Questions

• Would a coverage of parcels have dangling nodes?
• When would arcs cross each other but not have a
  node?
• What kinds of nodes would one have in a stream
  network?
• Why must the arcs of a polygon close?

22
(No Transcript)
23
Tiger file Design Street Segments
24
Crime Mapping Applications

• Points
• Location of a crime robbery , burglary
• Location of an arrest prostitution
• Location of an offender Megans law
• Lines streets where crimes occur , traffic
  violations, etc.
• Polygons neighborhood, park, gang territory,
  Census areas, etc.

25
The basic Crime Mapping Problem

• A crime or crime and arrest occurs at a specific
  location street address
• Traditionally we find the address and put a pin
  on a paper map
• Tedious time consuming possibility of error
• Also static

26
GIS Address Geocoding is Developed

• Match an address to a specific street location
  electronically MapQuest
• Census TIGER files are developed
• Topologically Integrated Geographic Encoding and
  Referencing system ???
• Intended for tabulation of Decennial Census forms

27
Tiger file Design Street Segments
28
The Address Geocoding Process

• Step 1 .. Build an address matching data base
  from TIGER line files
• Step 2 .. Build an address data file
• Street address
• Zip code (If needed) separate data column
• Crime type
• Time of crime
• etc. any other data specific to the crime

29
The Address Geocoding Process

• Step 3 Run the geocoding process to match
  addresses to street locations
• Step 4 Check and correct any addresses that the
  system cannot find.
• Result
• Points on a map representing the locations

30
Where is 1150 Main Street
31
The Address Geocoding Process

• Possible problems
• Multiple points in one location will show as
  single points no area
• Points for PO boxes will not be found
• Possible error in the estimation of where on the
  street.

32
The Raster Data Model

• The area in question is represented by grid cells
  sometimes called pixels
• Each cell is assigned a unique value
• The model represents continuous data surfaces.
• Elevation Vegetation cover
• Temperature Crime Hotspots

33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
Crime Hotspots
40
Crime Hotspots
41

• crj515_3b.ppt

42

• http//inquirer.philly.com/graphics/homicide_map_2
  007/