2. GETTING STARTED WITH GIS
2. GETTING STARTED WITH GIS
What are geographic information systems and what are they used for? ArcGIS: ArcMap, ArcCatalog and ArcToolbox Vector data vs. raster data vs. attribute tables Polygons, polylines, points Geodatabases
Geographic information systems (GIS) integrate hardware, software and spation data for capturing, managing, analysing and displaying all forms of geographically referenced information. GIS consists of computer hardware, software, spatial data, application method and people Used for: o map where things are e.g. roads in Sydney o map quantities e.g. obesity rates by US county o map densities e.g. population density in Sydney o spatial analysis find what’s inside e.g. how many dolphins inside the Marine Protected Area o network analysis find what’s nearby e.g. where’s the nearest doctor? o Map change (predictive modeling) e.g. current (a) and future (b-g) potential distributions of Dispar compacta: the extent of change in future distributions varies between climate models and projections GIS Software called ArcGIS 10.2 and is a software package o ArcMap: main application component of ArcGIS, and is used to view, edit, create and analyze geospatial information i. View and edit geographic data and create maps and graphs ii. Query your spatial data and perform some spatial analyses o ArcCatalog: is a file (map) management program, is used to move, create and store geospatial information i. Browse, organize, distribute, document o ArcToolbox: contains the geo-processing (analysis) applications i. All analyses is done in ArcToolbox ii. Contains lots of different analysis tools Two types of data used in GIS; Vector data: o Used to define objects with distinct boundaries e.g. roads, railway stations and property boundaries o Represent geography as points, polylines and polygons
o Provides a way to represent real world features o Vector features have attributes, consisting of text/numerical information that describe the features o File formats: Shape ‘file, comprised of several files (.shp, .shx, .dbf)
Raster data: o Used to define features and phenomena with a continuous surface and without a defined outline e.g. rainfall and elevation o Represent geography as cell matrices that store numeric values o Divides space into bricks, each cell represents a value in space e.g. 1mm, 1 degree – represent some characteristic o Commonly used for representing and managing imagery (e.g. aerial photography, satellite imagery) o Environmental phenomena that occur over a continuous surface o File formats: GRID – two or more folders Raster vs Vector Tables in GIS dBASE (.dbf) Benefits of Geodatabase o ability to store a rich collection of spatial data in a centralized location o maintain integrity of spatial data o work within a multiuser access and editing environment
3. COORDINATE SYSTEMS AND MAP PROJECTIONS Geographic vs. Projected coordinate systems
Decimal degrees vs. easting and northings Meridian, spheroids, datums – shape of the earth Map projection types (e.g. UTM) and distortions How to find, define and change (transform) coordinate systems
Cartesian coordinate system; o Two numbered lines intersect at right angles at their origins to form the axes of the coordinate system
o four quadrants, (x axis is horizontal, y axis is vertical) o Position of any point on the plain can be represented by an ordered pair of numbers (x, y) – the coordinates o Z-axis indicated depth Coordinate systems in GIS: GIS represent a model of the real world, accurately representing the spatial location of features. Coordinate (reference) systems enable every location on Earth to be represented by numbers/letters. Two different types, Geographic and Projected. Geographic Coordinate Systems o Use latitude and longitude to define the spatial location of features on the surface of a 3D model o Illustrated with a network of intersecting lines of latitude (parallels) and longitude (meridians) called the graticule. o Four components; 1. Angular Unit of Measure: Latitude and longitude are an angular measurement, measured in degrees (dms) Longitude = lines are called meridians, x axis, running east and west around the globe Latitude = lines are called parallels, y axis, running north and south around the globe 2. Prime Meridian: The zero value for longitude, official prime meridian passes through Greenwich, UK Zero value for latitude is always the equator 3. Reference Spheroid (or Ellipsoid) The Earth = is a geoid (bumpy etc) the earth approximates to an ellipsoid, a sphere flattened at the poles
4. Datums A reference spheroid (or ellipsoid) is a mathematically defined surface that approximates the size and shape of the earth. A datum defines the position of the ellipsoid relative to the centre of the earth Local or regional datum = moved spheroid to match the geoid over a specific region/country Global date = to match the world o Drawback of Geographic Coordinate Systems = don’t have a standard length, difficult to measure distance and areas accurately. To measure accurately, e need to convert the spherical earth to a flat map.
Projected coordinate systems o Projected coordinate systems transfer the information from the surface of a 3D to 2D o By converting (projecting) the latitude and longitude coordinates from a geographic coordinate systems (GCS) to planar XY coordinates – which specify a position in a plane (flat surface)
o Three components 1. Geographic coordinate system (starting point for transforming coordinates to a flat surface) 2. A linear unit of measurement to represent units on a planar surface (usually metres) 3. A map projection (mathematical transformation to convert geographic coordinates lat/long to planar coordinates) Differences between Geographic and Projected Coordinate system? o GCS describe locations on global 3D surface with lat/long values o PCS describe locations on a planar, flat 2D surface with x,y units – representing distance. Easting and northings = PCS. Map Projection – mathematical transformation to convert the earths 3D surface to map/computer screens 2D. A map projection can represent the whole earths surface or only a portion Types of map projections: o Cylindrical: ‘wrapping’ a flat surface over the globe to create a cylinder o Conic: setting a cone over the globe
o Planar: Flat o Polar – planar but on poles – shadows creating projection Distortions from representing earths surface in 2D: o Shape of any feature o Size (area) of any feature o The direction between a feature and surrounding features o The distance between a feature and surrounding features o Different map projections cause different types of distortion. There is not one perfect universal map projection. Each is designed to fulfill different requirements, choose the projection which best maintains the characteristic under study. o Types of Map Projection Types Equal-Area = preserve accurate area of features, distorts shape Conformal = preserve shape of features, distorts area Equidistant = preserves the distance between two features or points True Direction (Azimuthal) = preserve the direction between two features or points Compromise = attempts to balance shape and area distortion Universal Transverse Mercator System (UTM) solving distortion problems as you move away from the pole-to-pole line. System develops 60 unique pole-to-pole lines for anchoring this projection. Origins, false eastings and northings o The origin for each UTM zone is its central meridian and the equator o To eliminate negative coordinates, the coordinate system alters the coordinate values at the origin UTA/MGA Projection o Australian Map Grid and Map Grid of Australia coordinates are based on a UTM projected coordinate system o X (easting) has 6 digits
What are geographic information systems and what are they used for? ArcGIS: ArcMap, ArcCatalog and ArcToolbox Vector data vs. raster data vs. attribute tables Polygons, polylines, points Geodatabases
Geographic information systems (GIS) integrate hardware, software and spation data for capturing, managing, analysing and displaying all forms of geographically referenced information. GIS consists of computer hardware, software, spatial data, application method and people Used for: o map where things are e.g. roads in Sydney o map quantities e.g. obesity rates by US county o map densities e.g. population density in Sydney o spatial analysis find what’s inside e.g. how many dolphins inside the Marine Protected Area o network analysis find what’s nearby e.g. where’s the nearest doctor? o Map change (predictive modeling) e.g. current (a) and future (b-g) potential distributions of Dispar compacta: the extent of change in future distributions varies between climate models and projections GIS Software called ArcGIS 10.2 and is a software package o ArcMap: main application component of ArcGIS, and is used to view, edit, create and analyze geospatial information i. View and edit geographic data and create maps and graphs ii. Query your spatial data and perform some spatial analyses o ArcCatalog: is a file (map) management program, is used to move, create and store geospatial information i. Browse, organize, distribute, document o ArcToolbox: contains the geo-processing (analysis) applications i. All analyses is done in ArcToolbox ii. Contains lots of different analysis tools Two types of data used in GIS; Vector data: o Used to define objects with distinct boundaries e.g. roads, railway stations and property boundaries o Represent geography as points, polylines and polygons
o Provides a way to represent real world features o Vector features have attributes, consisting of text/numerical information that describe the features o File formats: Shape ‘file, comprised of several files (.shp, .shx, .dbf)
Raster data: o Used to define features and phenomena with a continuous surface and without a defined outline e.g. rainfall and elevation o Represent geography as cell matrices that store numeric values o Divides space into bricks, each cell represents a value in space e.g. 1mm, 1 degree – represent some characteristic o Commonly used for representing and managing imagery (e.g. aerial photography, satellite imagery) o Environmental phenomena that occur over a continuous surface o File formats: GRID – two or more folders Raster vs Vector Tables in GIS dBASE (.dbf) Benefits of Geodatabase o ability to store a rich collection of spatial data in a centralized location o maintain integrity of spatial data o work within a multiuser access and editing environment
3. COORDINATE SYSTEMS AND MAP PROJECTIONS Geographic vs. Projected coordinate systems
Decimal degrees vs. easting and northings Meridian, spheroids, datums – shape of the earth Map projection types (e.g. UTM) and distortions How to find, define and change (transform) coordinate systems
Cartesian coordinate system; o Two numbered lines intersect at right angles at their origins to form the axes of the coordinate system
o four quadrants, (x axis is horizontal, y axis is vertical) o Position of any point on the plain can be represented by an ordered pair of numbers (x, y) – the coordinates o Z-axis indicated depth Coordinate systems in GIS: GIS represent a model of the real world, accurately representing the spatial location of features. Coordinate (reference) systems enable every location on Earth to be represented by numbers/letters. Two different types, Geographic and Projected. Geographic Coordinate Systems o Use latitude and longitude to define the spatial location of features on the surface of a 3D model o Illustrated with a network of intersecting lines of latitude (parallels) and longitude (meridians) called the graticule. o Four components; 1. Angular Unit of Measure: Latitude and longitude are an angular measurement, measured in degrees (dms) Longitude = lines are called meridians, x axis, running east and west around the globe Latitude = lines are called parallels, y axis, running north and south around the globe 2. Prime Meridian: The zero value for longitude, official prime meridian passes through Greenwich, UK Zero value for latitude is always the equator 3. Reference Spheroid (or Ellipsoid) The Earth = is a geoid (bumpy etc) the earth approximates to an ellipsoid, a sphere flattened at the poles
4. Datums A reference spheroid (or ellipsoid) is a mathematically defined surface that approximates the size and shape of the earth. A datum defines the position of the ellipsoid relative to the centre of the earth Local or regional datum = moved spheroid to match the geoid over a specific region/country Global date = to match the world o Drawback of Geographic Coordinate Systems = don’t have a standard length, difficult to measure distance and areas accurately. To measure accurately, e need to convert the spherical earth to a flat map.
Projected coordinate systems o Projected coordinate systems transfer the information from the surface of a 3D to 2D o By converting (projecting) the latitude and longitude coordinates from a geographic coordinate systems (GCS) to planar XY coordinates – which specify a position in a plane (flat surface)
o Three components 1. Geographic coordinate system (starting point for transforming coordinates to a flat surface) 2. A linear unit of measurement to represent units on a planar surface (usually metres) 3. A map projection (mathematical transformation to convert geographic coordinates lat/long to planar coordinates) Differences between Geographic and Projected Coordinate system? o GCS describe locations on global 3D surface with lat/long values o PCS describe locations on a planar, flat 2D surface with x,y units – representing distance. Easting and northings = PCS. Map Projection – mathematical transformation to convert the earths 3D surface to map/computer screens 2D. A map projection can represent the whole earths surface or only a portion Types of map projections: o Cylindrical: ‘wrapping’ a flat surface over the globe to create a cylinder o Conic: setting a cone over the globe
o Planar: Flat o Polar – planar but on poles – shadows creating projection Distortions from representing earths surface in 2D: o Shape of any feature o Size (area) of any feature o The direction between a feature and surrounding features o The distance between a feature and surrounding features o Different map projections cause different types of distortion. There is not one perfect universal map projection. Each is designed to fulfill different requirements, choose the projection which best maintains the characteristic under study. o Types of Map Projection Types Equal-Area = preserve accurate area of features, distorts shape Conformal = preserve shape of features, distorts area Equidistant = preserves the distance between two features or points True Direction (Azimuthal) = preserve the direction between two features or points Compromise = attempts to balance shape and area distortion Universal Transverse Mercator System (UTM) solving distortion problems as you move away from the pole-to-pole line. System develops 60 unique pole-to-pole lines for anchoring this projection. Origins, false eastings and northings o The origin for each UTM zone is its central meridian and the equator o To eliminate negative coordinates, the coordinate system alters the coordinate values at the origin UTA/MGA Projection o Australian Map Grid and Map Grid of Australia coordinates are based on a UTM projected coordinate system o X (easting) has 6 digits
