Geographical Information System

Geographical Information System (GIS) is a tool for analysis and presentation of spatial data. It is a collection of computer hardware, software and geographic data for capturing, managing, analysing and displaying all forms of geographically referenced information.

What is GIS?

Simple definition 

A Geographic Information System organizes large volumes of raw data into a map form for easy comprehension.

GIS divides raw data into layers so it can give you a better understanding for the whole world.

A GIS is designed for the collection, storage, and analysis of objects and phenomena where geographic location is an important characteristic or critical to the analysis - this definition is broad and applies to a wide variety of methods for storing, accessing, and manipulating geographic information; it does not limit GIS to the computer environment .

Characteristics of a GIS

GIS stores:

• geographic coordinate data (spatial data)
• attribute data

Spatial data:

• represent features having known locations on earth
• one of: points (0D), lines (1D) or areas (2D)

Attribute data:

• non-graphic information linked to the geographical features (spatial data) describing features eg type of road, name, history.

Data layers and objects

• map data separated and stored in layers usually based on common geographical themes or data type
• alternative: objected-oriented GIS: geographical and all other information regarding a feature stored as an object

Formats

Two basic formats for storing and processing coordinate data: Vector and Raster

Vector:

• uses point locations (X,Y coordinate)
• advantage: less storage space
• disadvantage: may be more difficult to perform certain overlay functions

Raster:

• data stored as a matrix of pixels, representing points.
• to analyse or overlay multiple data layers, the layers must share a common projection and coordinate system, and layers must have topology established
• Disadvantage: it is necessary to store the entire matrix
• Advantage: can perform neighbourhood analysis easily

Why is GIS unique?

• GIS handles SPATIAL information
  • Information referenced by its location in space

GIS functions

• Data input
• Storage
• Management
• Analysis
• Output

Data input:

• keyboard entry, digitize maps; digital scanning (like a photocopy)

Storing data using Geodatabase

• Geodatabase is a container for spatial and non- spatial data that can be organized in a certain structure.
• Advantages:
  • provide a single, consolidated data storage for field measurements and all types of data used.
  • Controlling data entry by applying validation rule on the attributes.

Data management:

• database management system controls the way data are stored and retrieved
• includes verifying geographic coordinates and examining for accuracy

GIS analysis:

• create new data by manipulating existing data or analyzing relationships between sets of data
• basic operations: retriecal, map generalization, map abstractions, map sheet manipulation, map abstractions, map sheet manipulation, buffer generation, polgygon overlay and dissolve, measurements, digital terrain analysis and network analysis (Cox and wotshisface, 1997).

Output:

• display of output through printers and computer screens

CZM and GIS

• GIS stores all data relevant for the CZM
• GIS handles data on all spatial scales (North Egypt coast vs. a single harbour)
• GIS is a powerful analysis tool.
  • Comparison of measurements from different years
  • Overlay analysis of measurements and modelling results

Data types

Dfs1 Data MIKE 21

• DFS2 Data MIKE 21
• Dfs1 Data MIKE 21
• XYZ Data
• Wave time series & Rose
• Scanned Maps
• CAD drawing

CAD drawing

Additional Data

• Land use
• Sediment classification
• Satellite images
• Geographical maps
• Reports (design, licenses, Site investigation)
• ….etc.

External links

Wikipedia: GIS

GIS WWWW resource list of servers likely to be of interest to the GIS community

GIS dictionary

8th January, Ulrik Lumborg and Caitlin Pilkington (caitlin.pilkington@gmail.com), DHI.