GIS and GIS Data Model Flashcards
What does GIS stand for?
Geographic information system
GIS stores geographic information in
A database and displays it on a map
GIS maps are considered
Dynamic
A GIS store two types of geographic information
Feature and Attributes
Functions of GIS are
Visualization, geodata management, and geographic analysis
Why do people use GIS
To make decisions and solve problems
Data
a collection of facts from which conclusions may be drawn
Geographic Data
(a collection of) facts about a geographic entity (Earth’s physical features, inhabitants, and phenomena) from which conclusions may be drawn
Geographic Data Model
the methods of representation of geographical data into the computerized geographic information system.
The location of a geographic entity is linked to a geometry (point, line, poly, or a pixel), which refers to as spatial data.
Then the geometry is linked to its attribute(s).
An attribute could be quantitative or qualitative.
Types of Geographic Data
Geographic Data: - Spatial Data Is discrete, qualitive, continuous - Attribute Data Can be Qualitive or Quantitative, secrete and continuous.
Discrete Data
Integer Grids
Land use, Vegetation type, Roads, Wells
Continuous Data
Floating point grids
Elevation, Aspect, Pollutions, Rainfall
First Step Data is Prepared in
it uses points and their coordinates to represent spatial features as points, lines, and polygons
Dimensionality and property distinguish the point, line, polygons
Second Step Data is Prepared in
it organizes geometric objects and their spatial relationships into digital data files that computer can access, interpret, and process
The Level Of Detail In The Database Is Guided By
The scale of consideration
e.g.: A city at 1:1,000,000 may appear as a point, but at 1: 24,000 it will be an area
Dimensionalities and Properties of
Point
No length, width or height, only location implied
Defined by x, y coordinates
Also called a node or vertex
Dimensionalities and Properties of
Line
defined by a set of connected points
One-dimension, length, determined by the distance between the end points
Lines also known as edges, links
Examples: roads, streams, contour lines
Dimensionalities and Properties of
Polygon
wo-dimension, length and width give area and perimeter
Boundary is defined by a set of lines
Examples: political entities, water bodies
Point’s coordinates and Spatial Relationships
Coordinates are most often pairs (x,y) or triplets(x,y,z, where z represents a value such as elevation).
Topology
Topology is a mathematical approach of studying those properties of geometric objects that remain invariant under certain transformations such as bending or stretching.
When a Map is Stretched or Distorted
Some properties of objects are changed such as distance, angles, or relative proximities.
Topological Properties
Some properties won’t change,
Adjacencies and incidence
Spatial relationships, such as “is contained in”, “crosses”
Types of spatial objects - areas remain areas, lines remain lines, points remain points
A Spatial Database is often called “topological” if
Topological relationships have been computed, stored, and maintained such as
- connectedness of links at intersections
- ordered set of lines forming each polygon boundary
- adjacency relationships between areas
Elements of Raster Data Model and Feature Representation
Cell - also known as pixel
Cell value , Cell Size
Rows, number, Columns, number
Number of bands
Attribute table in raster dataset
