1 Flashcards
Definition of Geographical Information System
A Geographical Information System (GIS) is a powerful set of tools for collecting, storing,
retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes
- General definition: Tools that allow for the processing of spatial data into information
(and knowledge) - Technical definition: In a GIS, data about real–world objects is stored in a database and
dynamically linked to an onscreen map, which displays graphics representing real–world
objects (ESRI) - Geographical Information Science: The study of problems arising from the handling of
spatial information in Geographical Information Systems (entails finding solutions to
problems associated with the use of GIS) - Geographical Information and Society: Social context and the impact of GIS. Concerned
with the core issues as degree to which GIS empowers or disadvantages particular
groups
components of GIS
1. Users: All aspects of dealing with GIS involve interactions with humans. For the
operation of a GIS, the user needs to know how to handle a GIS (Technical Knowledge)
and must have advanced scientific knowledge of the subject under study.
2. Software: Their functionality is centered around four common types of actions.
*Data input: using existing digital datasets, field observations, and output of sensors (maps and images).
*Data storage and data management: the way in which data about location, linkages (topology),values/information (attributes) about geographical elements are structured and organized. The computer program used to organize databases is known as a database management system (DBMS), and the structuring of complex spatial data will be based on formal data models.
*Data output and presentations:
the ways to display data and present the results.
*Data transformation: needed to remove errors from data and to achieve answers to the questions asked to the GIS.
3. Hardware: The hardware provides computing capacity and data access needed for all actions of the software. Devices range from mobile or handheld to stand–alone
computers to complex server client networks involving many linked units. Physical size, computing power and memory are important. Peripheral hardware is included such as
digitizing tablets, scanners and printers.
4. Spatial data: There are 4 main components of spatial data:
1. Geometry: represents the geographical features (points, lines, polylines, polygons) associated with the real-world object.
2. Attributes: descriptive characteristics of geographic features.
3. Topology: considers spatial relationships; examples are connectivity and adjacency.
4. Behavior: means that geographic features can be made to allow certain types of editing, display, or analysis, depending on circumstances defined by the user.
four main components of spatial data (streets)
- Geometry represents the geographical features (points, lines, polylines, polygons) –>LINES
- Attributes: descriptive characteristics of geographic features. –> STREET NAME, LENGTH
- Topology: considers spatial relationships; examples are connectivity and adjacency. —> STREET A CROSSES STREET B
- Behavior: means that geographic features can be made to allow certain types of editing, display, or analysis, depending on circumstances defined by the user. –> THE STREET CANNOT HAVE MORE THAN 4 LANES
Explain the differences between vector and raster data models.
1. Vector data
- stores positional coordinates for each shape.
- most frequently used data model
- can be divided according to one of the three basic geographical data primitives: Pont, line, polygon
+ less storage space, because many pixels do not need to be stored in homogenous areas
+ Easier to associate a variety of descriptive resource data with a single resource feature
+ vector data set graphics tend to be of higher resolution (quality)
- Processing algorithms are complex
- Vectorizing scanned data needs high computational power
2. Raster Data
- uses a grid of square cells to represent real word entities
- the size of a single pixel determines the resolution
+ Neighborhood relations can be easily analyzed
+ Processing algorithms are easier than vector algorithms
- size of cells limits the resolution
- higher need of storage space compared to vector data
metadata
- Data about data
- gives descriptive information about data (such as source, resolution, availability, age, ownership, price, copyright and others, incl. information about data structure, creator, geographic extent, units and coordinate system.
- They give credibility to spatial data and in most cases data cannot be interpreted and used without Md
What operations should a GIS be able to perform?
1. Capture data: GIS must provide methods for entering geographic (coordinate) and tabular (attribute) data
2. Querying data:
- A GIS must provide tools for finding specific features based on their location or attributes.
- Queries, which are often created as logical statements or expressions, are used to select features on the map and
their records in the database.
- Suppose you wanted to find landlocked countries with a population
greater than 20 million. You would create a query expression with
those criteria. When the GIS finds features that meet the query’s
criteria, it highlights them on the map.
3. Analyzing data: Analyzing data:
▪ Proximity: GIS uses a process called buffering to determine the proximity relationships between features.
Example:
Proximity analysis uses the distance between features to answer questions like:
* How many houses lie within 100 meters of this water main?
* What is the total number of potential customers within 10
kilometers of a store?
* What proportion of the alfalfa crop is within 500 meters of the
well?
▪ Overlay: Integration of different data layers involving a process called overlay. It can be used to integrate data on soils, slope, vegetation, etc.
▪ Statistical/Geostatistical: Used to transform point data to areal data. Examples
are Inverse Distance Weighting or Kriging.
4. outputting data: GIS displays data in different ways. The more output options a GIS can
offer, the greater the potential for reaching the right audience with the right
information. Examples: Paper, internet, image, embedded in documents.
how is spatial data organized in a GIS?
Core of GIS: geographical database
–> collection of spatial and desciptive attributes of real-world entities (can be abstracted into 3 primary shapes: point, lines/polylines and polygons –> “feature types, feature classes, geomatric pbjects
–> each feature has an record in an attribute table
–> A unique identifier (FID) links feature with its attributes (–> attribute table: ex. 4110 FID + shape, area etc.)
- Collection of thematic layers that can be linked by geographic cooridinates.
- Each layer contains features having similiar attributes, like streets or cities, that are located within the same geographic extent. (also called Data frames)
