Introduction

What is GIS?

A computed-based information system that enables capture, modeling, storage, retrieval, sharing, manipulation, and presentation of geospatial data

• context: the structure of interrelationships between dataand how data is collected, processed, used, and understood within an application
• data is only useful within its context information = data + context

GIS functionality

• resource inventory
• field-based analysis: variations of attributes over a region
• network analysis:
• distributed data
• terrain analysis
  • visibility Analysis
• layer-based analysis
• location analysis
• spatiotemporal information

Data and databases

• data is measured in bits
• each bit records one of two possible states(0 or 1)
• Bits are merged into bytes
• each byte represents a single character
• each byte allows for 2^7=127 possible character combinations
• spatial data is traditionally divided into two great classes:
  • raster: ara array of grid of cells, referred to as pixels
    • pros: easy to handle,able to represent a large range of computable spatial objects
    • cons: inefficient in storing
  • vector: a finite straight line segment defined by its end points
    • pros: efficient in storing
    • cons: hard to analysis
• Database: a repository of data, the process of developing a database is a process of model building
  • application domain model: describes the core requirements of users in a particular application domain
  • conceptual model: tailored to a particular type of implementation
  • physical computational model: the result of a process of programming and system implementation
• spatial data retrieval and Analysis
  • spatial data is notoriously large and often hierarchically
  • geospatial data is often embedded in the Euclidean plane-> spatial storage structures + access methods
  • Map-based presentation is a distinctive feature of a GIS
• Distributed database: multiple databases connected by a digital communication network.
  • Increased reliability
  • improved performance

Hardware support

• input
• control
• storage
• processing
• digital networks: most communication networks are digital(0,1)
• analog network: for old data communication, signal strength can vary continuously like a sine wave
• Electromagnetic radiation
  • frequency
  • wavelength
  • higher bandwidth means greater data transmission capacity
  • High-frequency ultraviolet, X-rays, and gamma rays are not used for data transmission