AGR638 C3

• GIS (Geographic Information System)


  An electronic map

  
• GIS


  A system of computers, software, personnel, peripheral equipment, and data that allows the user to identify complex spatial relationships

  
• Computer


  • Must be dumb, fast, accurate
  • Maximum memory storage for RAM, disk storage, and backup storage needed
  • Data storage must be capable of secure, fast access, and have portability of sharing
  • Network capabilities, whether Ethernet or wireless must be available
  • A large monitor and large graphics card are also must since we will dealing with large amount of visual and graphic material
• Data


  • Digital maps, underlying list of attributes and values, and the image of the area study
  • The compilation of all the mappable objects into digital maps and their characteristics into a database provides the basic for analysis and thus our decisions
  • Data collection has been said to be 80 percent of the time commitment of a GIS

  
• Peripherals


  Pieces of equipment that support the computer and the GIS and allow a variety of input, output and storage options
• Input


  • Information
  • Field data is one important source of information
  • Handheld GPS is valuable devices to collect data and map field objects
  • The data can be downloaded through a docking station and portable media storage unit from the handheld device into a GIS

  
• Digitizing a paper map

  1. Mounting the map on a specialized digitizing table

  2. Using a special mouse-like "puck" to trace the boundaries of objects from paper map to create a digital copy

  3. Scanning the paper map to create a digital image of the map
• Digitizing an aerial photo

  1. Georeferencing the photo by identifying the coordinates of visible permanent objects using a GPS unit

  2. Tracing objects of interest on the digitized and georeferenced photo with the puck on the digitizing table, with the tracing being copied into a digital GIS map

  
• Output


  • The most obvious output device is a printer
  • High quality printer is in its ability to provide a high quality interpretive map
  • The main specification that a user should be aware of when looking printer is Its DOTs PER INCh (dpi)
• Storage


  • Sharing data by networks and USB devices
  • Memory sticks, secure digital cards, compact flash disk
• Personal


  • A CAD (Computer Aided Drawing) specialist or a network administrator are being commonly assigned to be the GIS specialist
  • The data analysis and interpretation is an art and a science, requiring someone who knows and enjoys computer, and also understands statistics and some technical aspects to which it will be applied

  
• GIS software


  Consists of two components: the Database Component and the Map Component

  
• Map Component


  • Allows the user to view representations of spatial objects or visualize the results of converting data to information
  • It is the compilation of map layers
  • Each map layer is a digital representation known as feature of an object or type of object
  • Each layer will contain from one to thousands of individual features representing real-world objects

  
• GIS layers


  • Not just confined to spatial objects, special events can also be mapped
  • An event is an action or occurrence that happen once or over time and can be recorded

  
• Special events mapped by GIS


  • Rainfall
  • Earthquake
  • Yield map

  
• GIS database


  • Stores, organizes, retrieves and analyzes data
  • Appears in spreadsheet form, with each row being a feature displayed on the map and each column being an attribute of the map layer's object data value entered for each individual feature

  
• Functions of GIS


  • Storage of Data
  • Retrieval of data
  • Manipulation
  • Analysis

  
• Retrieval of Data


  Query is the most common method, allowing to question the data and specify particular values or range of values for a selected attribute
• Manipulation


  Joining databases, both table joins and spatial joins, to combine aspatial and spatial data
• Analysis


  • The step taken by the user to establish a relationship between layers of data
  • Mathematical operations like addition, multiplication, subtraction, division, average, standard deviation etc. can be used to process the values found in database
• Field Calculator


  A GIS tool that can be used for a variety of algebraic and statistical functions on the data within the database
• Example GIS Software


  • ESRI (produces scalable and robust products)
  • ArcReader (allows viewing of spatial data)
  • ArcView (adds many analysis functions)
  • ArcEditor and ArcInfo (more advanced software for GIS specialists)
  • ArcGIS (the parent software suite)