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
Raster data represent
points by a single cells,
lines by sequences of neighboring cells,
and
areas by collections of contiguous cells.
Raster dataset attribute tables
Some raster datasets contain attribute tables
Typically cell values can represent or define a class, group, category, or membership
Cell Values in Raster data
Cell values can be Integer or Floating-point
Integer
Number with no decimal digits
Used for representing categorical data or discrete data
e.g.: land use, forest category, soil type
Floating Point
Number with decimal digits
Used for representing continuous data
Require more computer storage space
e.g.: precipitation, slope, DEM
Attribute Data Measurement Scale
Lowest to Highest
- Nominal
- Ordinal
- Interval
- Ration
Nominal
data are qualitative only,
no computation possible
Ordinal
qualitative or quantitative,
represent an order of the individuals
Interval
quantitative only
a zero entry simply
represents a position on a scale
Ration
Interval type with a meaningful zero entry
a ratio of two data values can be formed so one data value can be expressed as a ratio of the other.
Metadata
The term refers to any data used to aid the identification, description, quality, reference information, entry information, distribution information and data authority, etc. of geospatial data.
Evolution of Vector Data Model by ESRI systems
PC Arc/Info Workstation (1980s)
ArcView (End of 1990s)
ArcGIS 8 & 9 (2000s)
ArcGIS 10.x (2010)
Based on the georelational data model, an Arc/Info Coverage has two components:
A set of graphic files for spatial data and
A set of INFO files for attribute data.
The label connects the two components through feature ID
Arc/Info Coverage Data Structure
“Coverage” is the name of a GIS data layer in ESRI Arc/Info data structure.
“Coverage” maintains topological properties in spatial data structure
Collection of multiple Coverage is called a workspace
A “Coverage” in Arc/Info data structure is like a Folder, that contain a number of files.
Some of the files represent spatial feature geometry,
Some files for attribute data, and
some others for holding other information, such as maximum spatial extent, annotation, projection parameter, etc.
Two Versions of Coverage
an arc (line) file,
annotation for the line,
a tic file.
Shapefile Structure
Also known as ESRI ArcView Shapefiles.
Geographic features in a shapefile is also represented by points, lines, or polygons (areas)
File-based based data
collection of graphic and info files
same file name but different extensions (suffixes)
What is a Geodatabase
Is an object-based data model
The Geodatabase model is a collection of objects, properties and methods held in
a common file system
a Microsoft Access database
or a multiuser relational database
e.g.: Oracle, Microsoft SQL Server, or IBM DB2
Feature Geometry In Geodatabase
Point Feature
represented as single point or multi-point set of points
Feature Geometry In Geodatabase
Polyline Feature
a line or a set of line segments, which may or may not be connected.
e.g., user-shaped, curves, single / multi part
Feature Geometry In Geodatabase
Polygon Feature
a set of one or many rings. a ring is a set of connected, closed, non-intersecting line segment.
e.g., single / multi-part
Feature Class
Stores spatial data of the same geometry type
Can be broken down into subtypes
Feature Dataset
Stores feature data classes that share the same coordinate system and area extent
Feature classes included in a feature dataset ‘share’ topological relationships with each other
Contains different theme layers, multiple dataset
Standalone feature class
Feature class that is not included in a feature dataset
