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gis_basics.pptx - UNBC GIS Remote Sensing Lab


									GIS BASICS
 Location of update syllabus
 Hello Terrace
 Discuss the lab
 ◦ Questions
 Some maps
 GIS Basics
 ◦ Vector\Raster
 Properties of GIS Data
 Scale
 Precision
 Georeferencing
The GIS map known around the
world ...
                 Dr. John Snow (the
                  Father of Modern
                 1854-Snow create a dot
                  map by overlaying locations
                  of cholera patients with a
                  city map to determine the
                  source of the outbreak.
                  This turned out to be a
                  specific hand pump.
Okay not specific to GIS, but a
great “map”
 Minard’s Map -Napoleon's March to Russia
ESRI Mapbook
 ESRI Mapbook
Is this a map?

 FlightAware
GIS Basics
GIS Basics – 4 components of a
Data ...

Acquisition (Input)



Display (output)
Acquisition (Input)
 A data input subsystem allows the user to capture,
  collect, and transform spatial and thematic data
  into digital form. The data inputs are usually
  derived from a combination of hard copy maps,
  aerial photographs, remotely sensed images,
  reports, survey documents, etc.

   Most data that is used in this class already exists in some
   form. However, students will be creating their own data
   to input into their GIS.
Input Methods
 Manual Digitizing (vector)
 ◦ Heads up digitizing
 ◦ Digitize off a Geo-referenced image
 Scanning (raster)
 Remote Sensing (raster)
 Existing Digital Data (vector and/or raster)
 ◦ Digital Base Maps (vector)
 ◦ Databases
So what is the input data composed

 Spatial data (where) is displayed as layers or

 Aspatial data (what, how much, when)
 ◦ comes in the form of tables that can already exist
   with, be joined to spatial data.
 ◦ Describes the charactersitics of the spatial data
So what is the input data composed

 Spatial Data come in 2 formats;

 Raster/Image

 Vector
Vector Data                    (another ESRI definition)

 [data models] A coordinate-based data model that represents geographic
  features as points, lines, and polygons. Each point feature is represented as a
  single coordinate pair, while line and polygon features are represented as
  ordered lists of vertices. Attributes are associated with each vector feature,
  as opposed to a raster data model, which associates attributes with grid cells.
  (ESRI GIS Dictionary)

                                   Lines start and end with a node. At
                                   each change of direction in the line
                                   is a vertex. Vertices define the
                                   shape of a line or polygon

                                   The start and end node of a polygon
                                   is at the same location
Vector Data – Point, Line, Poly
                  Points (0 Dimension)
                   ◦ Display data as a single location
                   ◦ Has neither length or area
                  Lines (1 Dimension)
                   ◦ Sequence of xy coordinate pairs
                   ◦ Displays length at any given
                  Polygons (2 dimensions)
                   ◦ Connected sequence of xy
                     coordinate pairs
                   ◦ Displays area at any given scale
Vector Data and layers
 Layers contain features of a similar geometry

 ◦ A layer will not contain a combination of point and
   line features, point and poly, line and poly.
 Raster/Image Data
   [data models] A spatial data model that defines space as an array of equally
    sized cells arranged in rows and columns, and composed of single or
    multiple bands. Each cell contains an attribute value and location coordinates.
    Unlike a vector structure, which stores coordinates explicitly, raster
    coordinates are contained in the ordering of the matrix. Groups of cells that
    share the same value represent the same type of geographic feature. (ESRI GIS

Vector Data (advantages/disadvantages)

                                        Vector Data
                                                       Taken from
Raster Data (advantages/disadvantages)

                                                     Taken from
•The data management and retrieval subsystem organizes the data,
spatial and attribute, in a form which permits it to be quickly
retrieved by the user for analysis, and permits rapid and accurate
updates to be made to the database.

•This component usually involves use of a database management
system (DBMS) for maintaining attribute data. Spatial data is usually
encoded and maintained in a proprietary file format.
1. How data is stored and retrieved.

2. What information is within our layers and
   how relevant is it.

3. Managing data according to client

 Management will include the automation of
  data processes.
 What management tool have you been
  exposed to in the labs?

 ArcCatalog
   The data manipulation and analysis subsystem allows the user to define and execute spatial and attribute
    procedures to generate derived information. This subsystem is commonly thought of as the heart of a GIS, and
    usually distinguishes it from other database information systems and computer-aided drafting (CAD) systems.

example: where to locate a new school
based on …

>   impact on current land use,
>   low slope areas,
>   near recreation facilities and
>   distance from existing schools

 To date the primary analysis technique used in GIS applications, vector
  and raster, is the topological overlay of selected data layers.
Data output
 Maps, Tables, Charts
 Questions

 Hi Terrace
Properties of GIS Data
Spatial Data – Allows us to ask where is it

Attribute data - allows us to ask the question "what is it ?"

    •Every layer has an associated table
    •These are linked to spatial data by a feature code number
    Attributes are stored in columns as items
    •Rows display the attributes for each feature and are known as
    •entries may be text, integer, float (decimal) or date

Spatial Relationships – allows us to see patterns of features with
other features
Types of questions a GIS can help answer

a. Location: WHAT exists here - what is at a particular location?
   "What is at this location ?" e.g. Forest attributes or municipal ownership.

b. Condition: WHERE are specific conditions -
     where are all houses owned by person x?

c. Trends: WHAT HAS CHANGED (over time) -
    How far has the river bank receded in the past 2 years ?
    Where have houses increased in price by > 50%.

d. Patterns: HOW are features related
   "How does proximity to salmon streams affect the number of bear

e. Modelling: WHAT IF ..? -
   What if the climate warmed by 2 degrees? (effect on habitats)
Scale and Precision
Scale = the amount of reduction (expressed as a ratio)
e.g. 1:10,000 => a reduction in size / detail by 10,000 times

conversion to scale statement  => 1cm = 10,000cm (or 1cm = 100m)

A larger scale is thus reduced by a lesser amount.
1:50,000 is a larger scale than 1:250,000    (medium)
1:250,000 is a larger scale than 1:1,000,000 (small)

Data created at one scale are not suitable for different scales:
• At smaller scales, large scale data  are too complex
• At larger scales, small scale data are too generalized

For varying scales, see data on these two BC online mapping websites: or
  Precision is based on scale – how exactly can a coordinate be specified
  On printed maps, this was equivalent to ~ 0.5mm
  (= 25 metres at 1:50,000 … or 125 metres at 1:250,000)

GIS software uses ‘double-
precision’ giving up to 6
decimal places of meters

In most cases, this is bogus as
not warranted by the data
Further reading on GIS basics:
Data formats
File formats
 Stored in a variety of formats
 Maintain the same basic principles of “PLP”
 Lab work will focus on 2 formats common to
  ESRI products
 ◦ Shapefiles
 ◦ Coverage

 ◦ Personal and file geodatabases are another
   preferred data format for. We will look at this at a
   later date.
 Shapefiles (ESRI) Arcview

 .shp Spatial data                   e.g. rivers.shp
 .shx Index link file               e.g. rivers.shx
 .dbf Attribute data               e.g. rivers.dbf

   Also:
 .prj Projection file
 .sbn and .sbx .. optimise spatial queries


 Coverage (ESRI) - Arc/Info
 Layer name folder e.g. roads (spatial)     : 6-10 files
 Info folder                  (attributes): many files

 Multiple files per layer – zipped into one export .e00 format
Other Data formats
 Computer assisted drafting formats:
   ◦ .dxf (Autocad)
   ◦ .dgn (Microstation)

 Raster formats:
   ◦ .tif
   ◦ GeoTIFF

 Full list for ESRI
  List of data formats supported by ArcGIS

 Many more can be converted with FME (Feature Manipulation Engine)
Managing files
 ArcCatalog is built specifically to manage GIS
 Managing files using Windows has some
  inherent risks.
Quick message
 Hello Terrace

 Amy Hillier. 2011. "Manual for working with
  ArcGIS 10" The Selected Works of Amy Hillier
  Available at:

How do we make sure all
our data layers line up ?

= linking a layer or
dataset with spatial

= lining up layers with
each other

=The process by which the
geometry of an image is
made planimetric
If the world was flat, we could use a simple coordinate system with 0,0
in the bottom left corner (or A1) … but alas it isn’t …

        The edge of the world …
                                        Geographic referencing

                              180 E/W
      PG: 54N, 123W
           [54, -123]

Geographic referencing is
suitable for storing global                            0, 0
datasets, but involves
negative values south and
west of 0, 0
                     Geographic referencing

Geographic is not decimal, it is sexagesimal

1 degree = 60 minutes
1 minute = 60 seconds

Decimal degrees: 58° 30’   = 58.5              30/60 = 0.5
Decimal degrees: 58° 36’   = 58.6              36/60 = 0.6
Decimal degrees: 58°36’36” = 58.61         36/(60*60) = 0.01

View decimal degrees on pgmap website (use Internet Explorer / Active X)
The main problem with geographic referencing
(for GIS data display and analysis)

- 1 degree longitude varies from 0 - 111 km   (the system is not ‘rectangular’ )
                             Local example from the phone book
2007 (OK) –scale is consistent     2008: horizontal scale is almost double
  Length of One Degree of Longitude            Length of a Degree of Latitude 

  Latitude     Kilometres      Miles         Latitude      Kilometres     Miles 

     0º         111.32        69.17             0º           110.57       68.71  

     10º         109.64        68.13            10º          110.61       68.73 

     20º         104.65        65.03            20º          110.70       68.79 

     30º         96.49         59.95            30º          110.85       68.88 

     40º         85.39         53.06            40º          111.04       68.99 

     50º         71.70         44.55            50º          111.23       69.12 

    60º         55.80          34.67            60º          111.41       69.23 

     70º         38.19         23.73            70º          111.56       69.32 

     80º         19.39         12.05            80º          111.66       69.38 

     90º          0.00         0.00             90º          111.69       69.40 

  1° Longitude is half the distance at 60N             1° Latitude = ~ 111km
Earth is not a perfect sphere, it is ellipsoidal .. earth is the 'Geoid'. 
The difference in the major and minor axes has been estimated since ~1830
 The latest should be the most accurate, using satellite technology.
The difference representing the amount of 'polar flattening' is about 1/300 .

                                                Estimated ellipsoids
                                                     Equatorial         Polar           
                                                     Radius a         Radius b    
                           Name             Date                                         Flattening
                                                     (metres)         (metres)              
                           WGS 84           1984     6,378,137        6,356,752        1/298 

                           International    1924     6,378,388        6,356,912        1/297   

                           Clarke           1866     6,378,206        6,356,584        1/295  

                           Everest          1830     6,377,276        6,356,075        1/301 

                        Each ellipsoid has a 'Datum'  =  "a set of values that serve as a
                        base for mapping“. For Canadian / North America, we use:
                            a. North American Datum, NAD27 (1927) based on Clarke 1866
                            b. North American Datum, NAD 83 (1983) based on WGS 1984
                        NAD27 was the datum for mapping over most of the 20th century
                        NAD83 is the datum for contemporary GIS / mapping
   Universal Transverse Mercator (UTM) System
   this bit is hard so pay attention …

 The world is divided into 60 x 6 º longitude strips - the width of each zone thus
 varies from 6 x 111km = 666 km at the equator to < 80 km at 84 ° N
 They are numbered 1 - 60 from 180 º W to 180 º E
180W                                                                                 180E
Canada: UTM zones
UTM coordinates – in metres        - this is the hardest part …
Northings (N): from the Equator – increase to the north (to
Eastings (E) – based on the zone Central Meridian at 500,000

Coordinates repeat for each zone
                                   In BC, eastings are usually between 300,000-700,000
UTM zone overlap: Topographic map with Geographic and UTM

UTM zone Eastings coordinates in BC are generally between 300,000 – 700,00
UTM coordinates may make more sense here :


    (use Internet Explorer / Active X)

    The UTM system works well for a local area – coordinates in metres
  BC: UTM zones

How do we deal with multiple UTM zones: Eastings coordinates switch from ~700,000 at
the east edge of one zone to ~300,000 at the west edge of the next (= same place)
                              Albers (conic) projection

e.g. Yukon Albers:
                                     BC Albers projection

Central meridian: 126 W

First Standard Parallel: 50N

Second Standard Parallel: 58:30N

Latitude of projection origin 45N

False northing 0

False easting 1000000 (1million m)
 Summary: BC mapping coordinates

BC geomatics industry ‘recognises’:

1. Geographic – latitude / longitude                  – for data storage

2. Universal Transverse Mercator (UTM): zones 7-11 - local / regional

3. BC Albers                                          - for provincial data

View all 3 on: (imap)     (use Internet Explorer-IE) [sometimes!]

View Geographic and Albers on           (use IE / Active X)
                                          Multiple coordinate systems

 Georeferenced data can be recognised by the coordinates
 e.g. Prince George

 Geographic:                 -123      54
 UTM zone 10:           512,000        5972,000
 BC Albers:           1,200,000        1000,000
 GIS software today can overlay these by projecting ‘on the fly’

                                                         Where these would plot if
                                                         not properly defined:
To be able to do analysis, layers
MUST be reprojected into the same
projection and datum
e.g. UTM -> Albers
NAD 27 -> NAD83

Key points
 GIS falls under the umbrella of Geomatics
 GIS is an automated process
 GIS involves spatial locations
 4 main components of a GIS are
 ◦   Acquisition (Input)
 ◦   Management
 ◦   Analysis
 ◦   Display (Output)

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