combines elements of

1
Geomatics

• combines elements of
• computer science
• database design
• software design
• geography
• map projections
• geographic reasoning
• mathematics
• mathematical topology
• logical analysis
• has tended to be Canadian and European

2
Alternative terminology

• geographic information systems
• properly emphasizes geographic component
• minimizes computer science
• spatial information systems
• perhaps focuses too much on information systems
• land information systems
• deals with the cadaster

3
Why consider new term(s)

• computer science issues are becoming much more
  critical
• role of database systems is becoming more
  critical
• SQL 3
• Open GIS efforts reducing role of proprietary
  systems
• focuses on analysis

4
Consideration of fundamental issues

• how is reality organized
• most of us assume that this is obvious
• BUT it isnt
• it has major implications of what we can do with
  data and how
• consider entity versus field
• not just a minor issue

5
Entity vs field (part 1)

• (some simple discussions more later)
• entity partitioning reality into divisible units
• this is a thing and thats not
• examples
• soil mapping unit
• forest stand
• city block
• neighborhood
• but how do you divide

6
Entity vs field (part 2)

• phenomena exists everywhere and is potentially
  different everywhere
• examples
• elevation
• soil pH
• number PPM of chemical in air
• how can you map continuous data that is
  everywhere different

7
Entity vs field (part 3)

• fields can be converted to entities
• all locations where soil pH gt 7 and all where lt 7
• entities can be represented by fields
• soil unit represented by pH of soil unit
• basically different spatial data used to
  represent
• raster vs vector
• different operations etc etc etc

8
Entity

• phenomena that cannot be subdivided into like
  units but can have components
• e.g. entity house
• cannot be subdivided into houses
• can be divided into rooms
• indivisibility based on the properties used in
  the definition
• entities can be very different as long as the
  definitional criteria are same
• e.g. lake
• can be big or small have pollution or not
• e.g. polluted late or big lake
• in this case the size or presence/absence of
  pollutants does affect entity

9
Entity versus object

• entity is conceptual organization of phenomena
• object is digital representation of a specific
  case of the entity
• more on this later

10
Types of data associated with (spatial) entities

• identifier (name, ID number, code number)
• position - may be coordinates (x,y) but might be
  an address, zip code
• spatial properties - distance to next entity,
  area, depth
• dont confuse a set of positional coordiantes
  with spatial properties
• spatial properties may use or be based on
  coordinates but are not the same thing
• attribute - defined characteristic - number of
  residents, pH

11
Attributes

• defined characteristic of an entity
• conditions/characteristics of entities which are
  not part of the definition
• pavement type is an attribute of the entity
  highway
• pavement type is part of the definition of the
  entity asphalt highways
• may be behavioral, functional or compositional

12
Attributes and entities

• entity - primitive unit (stream, factory)
• instance - specific occurrence (Buffalo River,
  Campbells Soup Plant)
• object - digital representation in computer of
  one or more instances
• spatial type - way entity represented in system -
  point, line, area
• attribute - characteristic of entity (stream
  flow, number of employees)
• attribute value - particular measure of attribute
  for instance (3300 cfs, 450 employees)

13
Spatial dimensions

• traditional types of spatial entities
• points - x, y coordinate pair dimensionless
• lines - sets of connected x,y coordinate pairs
• one dimension - length
• areas - sets of at least 3 x,y coordinate pairs
  that start and end at the same pair
• two dimensions - length and width
• volumes - sets of at least 3 x,y,z coordinate
  tuples
• three dimensions - length, width and depth

14
In fact (almost) everything has three dimensions

• only things that doing are conceptual things
• starting point for the survey of the NW territory
• it is usually only the map representation of
  things that can take on these characteristics
• map scale is related to spatial dimensions
• oils well at 1100,000 versus 1200 scale
• street at 124000 scale versus 11200 scale

15
Spatial entities representation in database

• Initial introduction
• general concept of database representation
• one or more tables
• each table representing one entity class (e.g.
  streams)
• each table has a set of rows and columns
• each row represents one instance of the entity
  (Buffalo)
• each column in row stores attributes about
  specific instance (width, CFS, or coordinates of
  points)
• columns may be positional attributes or others

16
Geometric elements

• generally geometric elements are what are stored
  and manipulated in a computer representation of a
  spatial entity
• some terms
• line segment straight line connecting two points
• string/polyline set of line segments
• chain set of line segments connected at nodes
  (also arc)

x
x
x
x
17
Geometric elements (part 2)

• node point that terminates a line or where line
  cross
• a single straight line segment that connects two
  nodes is a link
• link can also be called edge
• and an arc
• LT prefer to have arc defined as a set of points
  (not the lines) that defining a string
• may be spline curve or polynomial function

18
Geometric elements (part 3)

• ring
• class of features that begin and end at same
  point
• closed polyline or ring of strings
• ring of arcs
• ring of links
• ring of chains

19
Combinations of entity types

• different entity types can be combined in many
  different ways in
• queries
• complex entities (compound entities)
• transformations (more later)
• duals (more later

20
Combinations of entity types