GIS Lecture 1 & Lecture 2 pt. 1 Flashcards
GIS
A powerful set of tools used for; storing and retrieving at will, transforming and displaying spatial data from the real world, for a particular purpose.
Geographic information system
computer based information system used to enable; capture, modelling, manipulation, retrieval, analysis, and presentation of geographically referenced data
Basic Concepts of GIS
Input: process of converting data from paper maps into computer files
Management: data volumes can become large and a DBMS is required. Relational design is preferred. Data is stored in a collection of tables and common fields are used to link the tables together.
Query and Analysis: process of geographical analysis. Uses geographical features to look for patterns and trends. It uses buffering and overlaying techniques.
Visualization: maps are very efficient at storing information and communicating geographic info.
Manipulation: Issues of scale and transformation of data for display or analysis (temporary or permanent).
Components of a GIS
Computer systems and software: A number of elements are required to run a GIS, i.e a powerful processor, sufficient memory space, and large storage space, high resolution graphics, and data input/output devices.
Spatial Data: Characterized by information about position, connections with other features and details of non-spatial characteristics.
Data Management and Analysis Procedures: Data stored in points, lines and areas, generally managed by a database. Data then transformed for analysis i.e scale. Info then shown on output.
People and GIS: Many GIS are run by teams who understand the system and using their imagination create new outputs. Underused or misused systems can be present too.
Organizing Spatial Data
- A GIS organizes and stores information about the world as a collection of thematic layers that can be linked by geography
- Each layer contains features with similar attributes, like streets and cities, that are located in the same geographic extent
- This simple but powerful and versatile, concept has proven invaluable for solving real world problems (e.g. flood prevention, fire control, tracking delivery vehicles, modeling global atmospheric circulation)
Geoid
The shape that the surface of the oceans would take under the influence of earth’s gravity and rotation alone, without wind or tides. Surface extended through continents. All points on the geoid have the same gravitational potential energy. Gravity force acts perpendicular to any point on geoid.
Coordinates
- The features on a map reference of the actual locations of the objects they represent in the
real world. - The positions of objects on the earth’s spherical surface are measured in geographic coordinates.
- While latitude and longitude can locate exact positions on the surface of the earth, they are not uniform units of measure; only along the equator does the distance represented by one
degree of longitude approximate the distance represented by one degree of latitude. - To overcome measurement difficulties, data is often transformed from three-dimensional geographic coordinates to two-dimensional projected coordinates
Projections
A projection system transforms the curved surface of the Earth to a flat plane enabling the visualization of earth or parts of it at a wide variety of scales for different purposes. Distortions introduced. (Imagine peeling an orange peel into a map shape).
Distortions
Spatial Properties distorted: Distance, area, shape, direction. Choices made for properties to preserve. Distortion exists in all 2D flat maps. No map projection can preserve all these properties. Map projections classified based on the spatial property they preserve.
The Mercator projection is a cylindrical map projection, which preserves local angles and shapes but significantly distorts size and area, especially near the poles. Think truesizeof
Key points on Map Projections
- Projections are Mathematical transformations
- Scale is true only in certain places
- Many different types have been devised
- All map projections distort
- Distortion characteristics vary from projection type to type.
- Some types are better for some applications than others
- A few types are used widely
Why do we use Projected Coordinate Systems?
- Degrees of latitude and longitude are not consistent units of measure for area, shape, distance, and direction.
- You are making a map in which you want to preserve one or more of these properties: area, shape, distance, and direction.
- You are making a small-scale map such as a national or world map. With a small-scale map, your choice of map projection determines the overall appearance of the map, e.g. with some
projections, lines of latitude and longitude will appear curved; with others, they will appear straight. - Your organization mandates using a particular projected coordinate system for all maps.
How do we determine which projections to use?
- Which spatial properties do you want to preserve?
- Where is the area you’re mapping? Is your data in a polar region? An equatorial region?
- What shape is the area you’re mapping? Is it square? Is it wider in the east–west direction?
- How big is the area you’re mapping? – On large-scale maps, such as street maps, distortion may be negligible because your map covers only a small part of the earth’s surface. – On small-scale maps, where a small distance on the map represents a considerable distance on the earth, distortion may have a bigger impact, especially if you use your map to compare or measure shape,
area, or distance.
Components of Geographic Data
- There are 3 general components of geographic information; Geometry, Attributes, Behaviors.
- Each feature (line, point, polygon) corresponds to a record in the attribute table
Methods of Data Capture
Data automation: automatically record, communicate and process data ex, GPS
Data conversion: Ex. from vector to raster
Data transfer: Copying data from one pc to another. Copying data from one storage device to memory.
Data translation: Converting data to the form used by one system to another
Digitizing: Process of converting geographic features on an analog map into digital format.
Data Sources
Integration
Fusion
Interoperability
Interoperability
the capability of components or systems to exchange data with other components or systems (eg. using .tab extension in ArcGIS)
Fusion
similar to integration but may contain attributes that might not be in the original dataset (eg. marine biologists use bathymetric, meteorological and sea surface temperatures to combine animal tracking data)
Integration
combines data resulting in different sources and providing users with a unified view of these data (eg. aerial photos + SDI data from MITA + OSM data)
Key Elements of Spatial Data
- Location – without location data are useless in spatial analysis
- Attribute data – spatial data locate the geographic objects, attribute data describe them
- Consistency – missing information is a problem. It is the key to good data and reliable analysis
- Scale – refers to the representative fraction that indicates what distance a given measurement on the map corresponds to on the ground (generic/specific)
- Metadata – is the data about data
Spatial Data Structures
- The Spatial Data Structure is the physical way in which entities are coded for the purpose of storage and manipulation
- Data structures provide the information to reconstruct the spatial data model in digital form.
- There are diverse data structures but they can be classified by whether they are used to structure
– Raster data or
– Vector data
Attribute Table
- Describe Qualities associated with features
- Stored in tables
- Attribute type
- Field properties
- Need to be defined when creating a shapefile
- Choice of attribute type & associated settings affect storage and display
- Can have serious consequences for accuracy and efficiency of the underlying database
GIS Data
Is the most important component. It integrates spatial data with other data resources. Can use a DBMS, used by organizations & maintain data, manage spatial data.
