# Shared Flashcard Set

## Details

Geospatial
Test One
59
Engineering
09/15/2012

Term
 Formal Definition of GIS
Definition
 A computer system capable of capturing, storing, analyzing and displaying geographically referenced information; that is, data identified according to location
Term
 History of GIS
Definition
 1960s: - Canada Geographic Information System (CGIS) - Harvard Lab for Computer Graphics and Spatial Analysis - Environmental Systems Research Institute (ESRI) 1970s: - Landsat Satellite; IBM's GFIS - Odyssey GIS by the Harvard Lab ~ first modern vector GIS 1980s: - Arc/Info by ESRI, MapInfo - GPS became operational in 1985 1990s: - ESRI ArcView ~ Merging of GIS and GPS - GIS migration from workstation to PC 2000s: - Internet - Wireless
Term
 Component Framework
Definition
 GIS Components: - Hardware (input and output devices/equipment) - Software - People
Term
 Layer Framework
Definition
 Vector: line based, single points Rastor: based on an area, shaded pixels
Term
 Why is GIS important?
Definition
 A database management tool  A powerful analytical tool  An effective communication tool
Term
 What can you do with GIS?
Definition
 **Anything with a spatial component** - Environmental Research - Agriculture - Military - Emergency Planning/Public Health - Natural Resource Management - Business Development/Community Design - Utility Management - Anthropology/Archaeology **Be thinking of examples**
Term
 What is cartography?
Definition
 Study and practice of making maps or globes
Term
 Five Components of Cartography
Definition
 **what makes it the foundation of GIS** Datums Projections Coordinate Systems Data Visualization
Term
 What is a map?
Definition
 Representation, usually on a flat surface, of the whole or part of an area
Term
 Two Examples of Early Maps
Definition
 Catal Hyuk ~ 6000 BC Ga-Sur (Iraq) ~ 2500-3800 BC
Term
 Flattening Ratio
Definition
 An index of measuring how flat the ellipsoid is. And ellipsoid (a mathematical model) is used to approximate the size and shape of Earth. f = (a-b)/a f=1/298 (for Earth) a=equatorial axis b=polar axis **a and b depend on the selection of datums**
Term
 What is a datum?
Definition
 A model of the surface of the earth based on a surveyed network of physical points. Datum=Ellipsoid+Point of Origin
Term
 Why is a datum important?
Definition
 A datum approximates the shape of the earth. A datum defines the position of the spheroid relative to the center of the earth.  A datum provides a frame of reference for measuring locations on the surface of the earth.  A datum defines the origin and orientation of latitude and longitude lines.
Term
 Components of a Datum
Definition
 - the reference ellipsoid **Both the shape of the ellipsoid and the position relative to the Earth are important** - a set of survey points
Term
 Two Types of Datums
Definition
 - Earth-centered Datums ex. WGS84 - Local Datums ex. NAD27 **two bwcause the surface of the earth is not smooth**
Term
 Common Datums for US and World
Definition
 Most Common in US:  NAD27 - North American Datum of 1927 NAD83 - North American Datum of 1983 World Datum: WGS84 - World Geodetic System of 1984 (used for GPS)
Term
 What is a Coordinate System?
Definition
 Defines the location of a point on a planar or spherical surface
Term
 Why is a Coordinate System important?
Definition
 Provides a reference for locating objects on the spherical surface or flat surface
Term
 Common Coordinate System Examples
Definition
 DD vs DMS
Term
 What is projection?
Definition
 Sets of mathematical equations that convert coordinates from one system to another. Systematic transformations of spheroidal shape of the earth so that the curved, three-dimensional shape of a geographic area on the earth can be represented in two dimensions as x and y coordinates.
Term
 Why is projection important?
Definition
 Ideally, a 3D globe with accurate shape is the best approximation of the Earth, but globes are difficult to make, carry, update and make measurements on. Transforming from 3D to 2D will help solve these problems.
Term
 Two Main Types of Projections
Definition
 Distortion-Based: Conformal Projections Equal Area Projections Equidistance Projections Shape-Based: Conic Projections Cylindrical Projections Planar Projections  Azimuthal/Polar Projections
Term
 Two Common Coordinate System/Projections
Definition
 State Plane UTM ~ Universal Transverse Mercator
Term
 What is a scale?
Definition
 - A ratio between distances on the map and corresponding distances in the real world. - It's also an expression of how much the area represented has been reduced on the map. - Map scale is important for understanding maps both in paper and computer form.
Term
 Types of Scales
Definition
 Verbal Scale: expresses in words a relationship between a map distance and a ground distance (ex. one inch represents 16 miles) Graphic/Bar Scale: The most common found on maps Representative Fraction/Ratio Scale: (ex. 1/24,000 or 1:24,000)
Term
 Data Model
Definition
 Model that describes in an abstract way how data is represented in an information system or a database management system; generalized view of data representing the real world
Term
 Two Main GIS Data Models
Definition
 Vector: represent geographic phenomena with points, lines and polygon points Raster: matrix of cells
Term
 Components and Characteristics of Vector Data
Definition
 Components: Points Lines Polygons Characteristics: - "ArcNode" Topology: Arcs are composed of nodes and vertices, and arcs begin and end at nodes with vertices in between - Depends on Scale: a building can be represented by a point or a polygon depending on the scale of the landscape - Useful for representing and storing discrete features such as buildings, pipes or parcel boundaries - Has an attribute table associated with feature
Term
 Components and Characteristics of Raster Data
Definition
 Components: Matrix(grid) of cells, each with a width and height and is a portion of the entire area represented Characteristics:  - Cell size determines resolution: smaller cell size=more accurate but takes up a lot more storage space - Only one corner of the raster layer is georeferenced - Location of each cell is defined by its row or column location within the matrix - Represented by Cartesian Coordiante System with rows parallel to the x-axis, columns parallel to y-axis - Each cell has ONE value, which represents the property or attribute of interest - Values can be positive, negative, integer, floating-point, or even nodata - Gradation: (Lefthand column in ArcGIS) High Level to Low Level
Term
Definition
 Advantages:  - Good representation of reality - compact data structure ie doesn't take up as much room - Topology can be described in a network - Accurate graphics Disadvantages:  - Complex data structure ie requires very accurate data - Simulation can be difficult - Some spatial analysis is difficult or impossible to perform
Term
Definition
 Advantages:  - Simple data structure (ONE value) - Easy overlay with complex data - Good for various kinds of spatial or statistical analyses - Ability to uniformly store points, lines, polygons and surfaces Disadvantages:  - Inherent spatial inaccuracies due to cell-based feature representation (approximation) - Large amount of data, takes up a lot of storage space - Different scales between layers can be a nightmare - Information loss due to generalization
Term
 TIN Data Model
Definition
 Triangulated Irregular Network: - Data model that is used to represent 3D objects - Network of linked triangles drawn between irregularly spaced points with x, y and z values - Each triangle assumes a constant gradient. The slope and aspect for the x, y and z values at the three points that make up the triangle. - More complex than vector or raster data. - Efficient way to store and analyze surface.  - Should not be used for mountainous terrain, but rather flatlands because of constant gradient.
Term
 Vector Data Formats
Definition
 ArcInfo Coverage  ArcView Shapefile Geodatabase CAD
Term
 Raster Data Formats
Definition
 ArcInfo GRID DEM: Digital Elevation Model DOQ: Digital Othophoto Quadrangles Satellite Images Aerial Photos Scanned Maps Graphical Images (TIFF, JPEG, BMP)
Term
 Geodatabases
Definition
 - Latest format and preferred in ArcGIS - Relational databases that contain geographic information ie geographically referenced - Contain feature classes and tables - Store many different vector and rastor layers as well as tables, layer files, topographical relationship, models and more in a single database file - all feature classes in a feature dataset share the same coordinate system - can be easily shared among users, so much less code can be emailed
Term
 Two Types of Geodatabases
Definition
 Personal  Multiuser
Term
 DEM
Definition
 Digital Elevation Model - Most important - Consists of an array of uniformly spaced elevation data - Mostly developed by USGS, free data for US, Canada and Puerto Rico - Non-USGS DEM is LIDAR: different type, based on different projection - Global DEMs: GTOPO30, small cell size, NOT free
Term
 Shapefiles
Definition
 .shp .shx .dbf
Term
 GIS Attribute Data Types
Definition
 Nominal: categories, can be text or number; computing is nonsense Ordinal: rank, classification Interval: no absolute scale, ex. temperature Ratio: absolute value, continuous, one set porportion of other set Cyclical: used to characterize directional attributes
Term
 Main Sources of GIS Data
Definition
 Government Agencies: Federal, State and Local Commercial Data Venders The Internet Research Community  Yourself
Term
Definition
 - Data about data. - Information about a particular data set which may describe, for example, how, when, and by whom it was received, created, accessed and/or modified and how it is formatted. - Describes the content, quality, condition and other characteristics of the data.
Term
Definition
 - Metadata is vital in helping potential users to find needed data and determine whether a data set will meet their needs before they spend the time and money to obtain and process it.  - It is important for:  Data browsing/previewing Data transferring Data Documentation Data Searching
Term
Definition
 - Identification / Title - Data Quality - Spatial Data Organization (Publisher/Creator) - Spatial Reference - Entity and Attribute  - Distribution  - Contact  - Metadata Reference
Term
Definition
 - A variety of free and commercial software tools available to support metadata development - Tools for creating and editing metadata: Freeware/shareware, ArcCatalog - Metadata should be created to meet certain standards about structure and contents - The Content Standards for Digital Geospatial Metadata (CSDGM)
Term
 Formal Definition of GPS
Definition
 A global navigation system based on 24 or more satellites orbiting the earth at an altitude of 12,000 miles and providing worldwide positioning and navigation information 24 hours a day, in any weather.
Term
 Three Components of GPS
Definition
 Satellite Constellation (Space Segment) Ground Control Network (ground segment) User Equipment (User Segment)
Term
 Satellite Constellation
Definition
 - 24+ NAVSTAR satellites - Orbit: 20,200 km above the Earth - continuously broadcast position and time data - First satellite launched in 1978 - full constellation of 24+ satellites in operation in 1994 - At least 4 satellites are visible anytime, anywhere - Most locations usually have 6 to 8 satellites available - Each satellite makes roughly two revolutions per day
Term
 Ground Control Network
Definition
 - Maintains the system through five monitoring stations and a master control station at Shriver Air Force Base, Colorado - These stations correct orbit and clock errors
Term
 User Equipment
Definition
 Consists of the receivers, processors and antennas that allow land, sea or airborne operators to receive the GPS satellite broadcasts and compute their precise position, velocity and time
Term
 How does GPS work?
Definition
 - GPS sattelites circle the earth twice a day in a very precise orbit and transmit signal information to earth - GPS receivers take this information and use triangulation to calculate the user's exact location  - The GPS receiver can help determine locations on the Earth's surface by collecting signals from three or more sattelites through a process called triangulation  - Three spheres are necessary to find position in two dimensions - Four are needed in three dimensions
Term
 Some sources of GPS Errors
Definition
 - Ionoshpere and Troposhere delays: signal slows as it passes through atmosphere - signal multipath: signal is reflected off of tall buildings or rocks - receiver clock errors: not as accurate as atomic clocks - orbital errors: inaccuracies of reported location
Term
 How can signal errors be reduced?
Definition
 - Taking multiple measurements at the same location and then calculate the average - Differential correction (DGPS)
Term
 DGPS
Definition
 Differential Global Positioning System What: enhancement to GPS that a network of fixed ground based reference stations to broadcast the difference between the positions indicated by the sattelite systems and the known fixed positions How it works: These stations broadcast the difference between the measured satellite pseudoranges and actual (internally computed) pseudoranges, and receiver station may correct their pseudoranges by the same amount; basically uses a reference system Why: DGPS accuracy and integrity are better than GPS
Term
 ArcMap
Definition
 - Central application in the ArcGIS Desktop - Used for all map-based tasks including cartography, map analysis and editing - working with maps that each have a page layout containing a geographic window or view with a series of layers, legends, scale bars, north arrows and other elements - offers a different way to view a map (a geographic data view and layout view) in which you can perform a broad range of advanced GIS tasks
Term
 ArcCatalog
Definition
 - application helps you to organize and manage all of your GIS data - includes tools for browsing and finding geographic information, recording and viewing metadata, quickly viewing any dataset, and defining the schema structure for your geographic data layers
Term
 ArcToolbox
Definition
 - simple application containing many GIS tools used for geoprocessing - two versions: complete version with ArcInfo and the lighter version that comes with ArcView and ArcEditor software - lighter version contains over 20 commonly used tools for data conversion and management - complete version comes with a comprehensive set of tools (over 150) for geoprocessing, data conversion, map sheet management, overlay analysis and map projection
Term
 Major GIS Data Formats
Definition
 - Topographically Integrated Geographic Encoding and Referencing System (TIGER) - Digital Line Graphs (DLG) - Digital Elevation Model (DEM) - Digital Orthophoto Quadrangles (DOQ)
Term