Data models Flashcards
Two main Data Models/Data Structures
Discrete Objects
Continuous Fields
Discrete Object characteristics
objects:
- can be counted
- can hold a set of attributes
- distinguished by their dimensions
- naturally fall into the categories of lines, points and areas.
“areas” (discrete objects)
Objects that occupy area are termed two-dimensional
“lines” (discrete objects)
One dimensional lines (includes roads, railways, rivers) represented as one dimensional objects
“points” (discrete objects)
Zero-dimensional points, such as animals or buildings
Discrete objects
the ability of GIS to handle truly 3-dimensional objects as volumes with associated surfaces remains limited.
Continuous Fields
- generally only interested in one attribute (i.e. elevation/temperature) - can be distinguished by what varies and how smoothly, with gradual changes
When determining a cell’s identity when i9t occurs on a boundary, we use either:
Largest Share Rule
Central Point Rule
Largest Share Rule
Defining the identity of a cell depending on what makes up the largest share of that cell.
Central Point Rule
Defining the identity of a cell depending on the central point of that cell.
Point
A point has neither length nor breadth nor depth, hence it is said to be of dimension 0.
May be used to indicate spatial occurences or events and their spatial patterning.
Centroid
An artificial point reference, located so as to provide a summary measure of the location of the object.
Lines or Polyline
Have length, but not breadth or depth, and hence are of dimension 1.
Used to represent linear entities (roads, pipelines, lakes), or to measure distances between spatial objects.
Node
All lines have a minimum of two points, a beginning and an ending point, often referred to as nodes.
Nodes are also located at the intersection of two or more lines.
Vertices
Additional points placed between the beginning and ending nodes to give shape to the line.
