Something basic about GIS MingChun Lee What is

Something basic about GIS Ming-Chun Lee

What is GIS ? GIS = Geographic Information System Three components: ◦ Geography – the real world ◦ Information – data and information ◦ Systems – technologies

A Definition of GIS = Geographic Information System Worboys, 1995: ◦ A Geographic Information System (GIS) is a computer-based information system that enables one to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.

Functions of GIS Data Collection Storage & Management Retrieval Conversion Analysis Display

Applications of GIS How GIS can be used: ◦ ◦ ◦ ◦ Infrastructure Management Transportation Network Routing Floodplain Management Emergency Response Planning Noise Pollution Analysis Participatory Planning Processes Jobs/Housing Spatial Balance and more …

The GIS Data Model Administrative Boundaries Utilities Zoning Buildings Parcels Hydrography Streets Digital Orthophoto Data Organized by Layers/Themes

GIS Database GIS data is organized by Layers/Themes ◦ A Theme is a collection of geographic features (usually a separate file), such as boundaries, roads, together with the attributes (may stored in other files) of those features A set of Themes for a geographic area makes up a GIS Database (a group of files)

The GIS Data Model • Layers Integrate Using Explicit Location on the Earth’s Surface • Themes have to be georeferenced.

Georeferencing Identifying Locations on the Earth Using Locations on a Map or GIS Aspects of Georeferencing ◦ Coordinate Systems Geographic Coordinate System Projected Coordinate System ◦ Projections

Coordinate Systems A Method of Locating Objects on the Earth’s Surface Examples: ◦ Geographic (Global) Coordinate System ◦ Projected (Cartesian) Coordinate System

Geographic Coordinate System (GCS) uses a three dimensional spherical surface to define locations on the earth.

Geographic Coordinate System In the spherical system, horizontal lines are lines of equal latitude, or parallels Vertical lines are lines of equal longitude, or meridians. These lines encompass the globe and form a gridded network called a graticule

Geographic Coordinate System A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the earth’s center to a point on the earth’s surface. The angles often are measured in degrees (or in grads).

Measuring Latitude Measures the Angular Distance from the Equator North Pole (90 º N) Equator 60 º N 60 º South Pole (90 º S) Side View

Measuring Longitude n Longitude Measures the Angular Distance from the Prime Meridian (Greenwich, UK) 135 º E North Pole Equator 70 º W Prime Meridian (0 º) 135 º 70 º Top View

Projected Coordinate Systems A projected coordinate system is defined on a flat, two-dimensional surface. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid. In a projected coordinate system, locations are identified by x, y coordinates on a grid

Projection Whether you treat the earth as a sphere or a spheroid, you must transform its three-dimensional surface to create a flat map sheet. The Process of Systematically Transforming Positions on the Earth’s Spherical Surface to a Flat Map While Maintaining Spatial Relationships

Geometric Models for Projection Conical ◦ Tangent along a Specific Latitude ◦ Screen is a conic surface. Lamp at the center of the earth Cylindrical ◦ Tangent along Equator or a Longitude ◦ Screen is a cylindrical surface. Lamp at the center of the earth Planar/Azimuthal/Zenithal ◦ Tangent at a Single Point ◦ Screen is a flat surface tangent to the earth. Lamp at various positions

Map Projection and Distortion n For Geometric Properties Affected by Projection: n n n Shape or Angle Area Distance Direction All projections produce some distortion

Common Projection Systems Universal Transverse Mercator (UTM) State Plane (SP)

Universal Transverse Mercator Series of Cylindrical Projections, Tangential to a Longitude Line 60 Zones, One Every 6 Degrees Longitude Each Zone: ◦ Width is 6º in Longitude ◦ Height is from 80º S to 84º N in Latitude

State Plane Planar Projection ◦ Tangent at Different Points for Each State Most States Have Two or More Zones

Types of GIS Data Describes Objects In Terms Of: ◦ Spatial Data Absolute X, Y Coordinates – Locations Size, and Shape ◦ Attributes Characteristics associated with Geography

GIS Associates Spatial and Attribute Data in a Geo-Referenced Database ARC 1 5 2 4 INFO 3 ID 1 2 3 4 5 AREA 260210 18210 260210 258876 3008 PERIM CLASS LANDUSE 20688 100 Single Family 20688 100 Multi Family 20688 100 Commercial 16880 200 Forest 88 500 Water

Data models Data models: Formats in which geographic data is stored and managed. Vector Data Models (Features) ◦ Points ◦ Lines ◦ Polygons Raster Data Models (Surfaces)

Raster and Vector Data Models Raster Representation Vector Representation point line polygon

Raster Data Models Raster Data Model ◦ Location is referenced by a grid cell in a rectangular array or matrix ◦ Attribute is represented as a single value for that grid cell

Raster Data Models

Raster Data Models Raster Data Model ◦ Typical data sources: Images from remote sensing (LANDSAT, SPOT) Elevation data from USGS ◦ Best for continuous data: Elevation Temperature

Raster Data Model Uses Elevation Temperature Noise Levels Air Quality Distance or Accessibility Surfaces Probabilities (e. g. flooding, liquefaction) Photographic Images

Vector Data Models Vector Data Model ◦ Location is referenced by x, y coordinates, which can be linked to form lines and polygons ◦ Attributes referenced through unique ID number to tables

Features Geographic objects that have different shapes are represented as features

Features Points are a pair of x, y coordinates

Features Lines are sets of coordinates that define a shape

Features Polygons are sets of coordinates defining boundaries that enclose areas.

Vector Data Models Vector Data Model ◦ Typical data sources: DIME (Dual Independent Map Encoding) and TIGER (Topologically Integrated Geographic Encoding and Referencing file) files from US Census DLG (Digital Line Graph) from USGS for streams, roads, etc. ◦ Best for features with discrete boundaries: Soil Type Land Use

Vector Data Model Uses Land Use or Zoning Classifications ◦ Polygons Transportation Networks ◦ Points and Polylines Hydrology ◦ Polylines for Rivers, Polygons for Water Bodies Utilities ◦ Points for Facilities, Polylines for Pipelines & Wires

Raster Advantages & Disadvantages Raster Advantages ◦ Easy to Understand the Data Model ◦ Easy to Analyze ◦ Low Computing Requirements ◦ Compatible with Remote Sensing Sources ◦ Efficient for Continuous Data ◦ Easy to Use in Modeling Raster Disadvantages ◦ Spatial Inaccuracies Common ◦ Low Resolution, Relative to Vector Data ◦ Imprecise Locational Data ◦ Requires All Cells to be Coded ◦ Not As Efficient for Discrete Data or Features

Vector Advantages & Disadvantages Vector Advantages ◦ More Readable as a Map ◦ Higher Resolution than Raster Data ◦ Can Have High Spatial Accuracy ◦ Can Have Storage Advantages ◦ Can Be Topological ◦ Efficient for Discrete Data or Features Vector Disadvantages ◦ Difficult to Manage Data Storage ◦ High Computing Requirements ◦ Complex to Perform Overlay and Modeling Operations ◦ Inefficient for Continuous Data

Introduction to Arc. GIS is a software program , used to create, display and analyze geospatial data , developed by Environmental Systems Research Institute (ESRI) of Redlands, California. http: //www. esri. com/

ESRI’s Arc. GIS Platform Suite of Three Integrated Applications: ◦ Arc. Catalog ◦ Arc. Map ◦ Arc. Toolbox

Components of Arc. GIS Arc. Catalog is used for browsing for maps and spatial data and managing spatial data, viewing and creating metadata. Arc. Map is used for visualizing spatial data, performing spatial analysis and creating maps to show the results. Arc. Toolbox is an interface for accessing the data conversion and analysis function that come with Arc. GIS.