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GIS BASICS Agenda Location of update syllabus Hello Terrace Discuss the lab ◦ Questions Some maps GIS Basics ◦ Vector\Raster Properties of GIS Data Scale Precision Georeferencing The GIS map known around the world ... Dr. John Snow (the Father of Modern epidemology) 1854-Snow create a dot map by overlaying locations of cholera patients with a city map to determine the source of the outbreak. This turned out to be a specific hand pump. Okay not specific to GIS, but a great “map” Minard’s Map -Napoleon's March to Russia ESRI Mapbook ESRI Mapbook Is this a map? FlightAware GIS Basics GIS Basics – 4 components of a GIS Data ... Acquisition (Input) Management Manipulation Analysis Query Display (output) Acquisition (Input) A data input subsystem allows the user to capture, collect, and transform spatial and thematic data into digital form. The data inputs are usually derived from a combination of hard copy maps, aerial photographs, remotely sensed images, reports, survey documents, etc. Most data that is used in this class already exists in some form. However, students will be creating their own data to input into their GIS. Input Methods Manual Digitizing (vector) ◦ Heads up digitizing ◦ Digitize off a Geo-referenced image Scanning (raster) Remote Sensing (raster) Existing Digital Data (vector and/or raster) ◦ Digital Base Maps (vector) ◦ Databases So what is the input data composed of? Spatial data (where) is displayed as layers or features Aspatial data (what, how much, when) ◦ comes in the form of tables that can already exist with, be joined to spatial data. ◦ Describes the charactersitics of the spatial data So what is the input data composed of? Spatial Data come in 2 formats; Raster/Image Vector Vector Data (another ESRI definition) [data models] A coordinate-based data model that represents geographic features as points, lines, and polygons. Each point feature is represented as a single coordinate pair, while line and polygon features are represented as ordered lists of vertices. Attributes are associated with each vector feature, as opposed to a raster data model, which associates attributes with grid cells. (ESRI GIS Dictionary) Lines start and end with a node. At each change of direction in the line is a vertex. Vertices define the shape of a line or polygon The start and end node of a polygon is at the same location Vector Data – Point, Line, Poly Points (0 Dimension) ◦ Display data as a single location (x/y). ◦ Has neither length or area Lines (1 Dimension) ◦ Sequence of xy coordinate pairs ◦ Displays length at any given scale Polygons (2 dimensions) ◦ Connected sequence of xy coordinate pairs ◦ Displays area at any given scale Vector Data and layers Layers contain features of a similar geometry ◦ A layer will not contain a combination of point and line features, point and poly, line and poly. Raster/Image Data [data models] A spatial data model that defines space as an array of equally sized cells arranged in rows and columns, and composed of single or multiple bands. Each cell contains an attribute value and location coordinates. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are contained in the ordering of the matrix. Groups of cells that share the same value represent the same type of geographic feature. (ESRI GIS Dictionary) Raster Image Vector Data (advantages/disadvantages) Vector Data Taken from http://bgis.sanbi.org/gisprimer/page_19.htm Raster Data (advantages/disadvantages) Taken from http://bgis.sanbi.org/gisprimer/page_19.htm Management •The data management and retrieval subsystem organizes the data, spatial and attribute, in a form which permits it to be quickly retrieved by the user for analysis, and permits rapid and accurate updates to be made to the database. •This component usually involves use of a database management system (DBMS) for maintaining attribute data. Spatial data is usually encoded and maintained in a proprietary file format. Management 1. How data is stored and retrieved. 2. What information is within our layers and how relevant is it. 3. Managing data according to client specifications. Management will include the automation of data processes. Management What management tool have you been exposed to in the labs? ArcCatalog Analysis The data manipulation and analysis subsystem allows the user to define and execute spatial and attribute procedures to generate derived information. This subsystem is commonly thought of as the heart of a GIS, and usually distinguishes it from other database information systems and computer-aided drafting (CAD) systems. example: where to locate a new school based on … > impact on current land use, > low slope areas, > near recreation facilities and > distance from existing schools Analysis To date the primary analysis technique used in GIS applications, vector and raster, is the topological overlay of selected data layers. Data output Maps, Tables, Charts Questions Hi Terrace Properties of GIS Data Spatial Data – Allows us to ask where is it Attribute data - allows us to ask the question "what is it ?" •Every layer has an associated table •These are linked to spatial data by a feature code number Attributes are stored in columns as items •Rows display the attributes for each feature and are known as records •entries may be text, integer, float (decimal) or date Spatial Relationships – allows us to see patterns of features with other features Types of questions a GIS can help answer a. Location: WHAT exists here - what is at a particular location? "What is at this location ?" e.g. Forest attributes or municipal ownership. b. Condition: WHERE are specific conditions - where are all houses owned by person x? c. Trends: WHAT HAS CHANGED (over time) - How far has the river bank receded in the past 2 years ? Where have houses increased in price by > 50%. d. Patterns: HOW are features related "How does proximity to salmon streams affect the number of bear attacks"; e. Modelling: WHAT IF ..? - What if the climate warmed by 2 degrees? (effect on habitats) Scale and Precision Scale Scale = the amount of reduction (expressed as a ratio) e.g. 1:10,000 => a reduction in size / detail by 10,000 times conversion to scale statement => 1cm = 10,000cm (or 1cm = 100m) A larger scale is thus reduced by a lesser amount. 1:50,000 is a larger scale than 1:250,000 (medium) 1:250,000 is a larger scale than 1:1,000,000 (small) Data created at one scale are not suitable for different scales: • At smaller scales, large scale data are too complex • At larger scales, small scale data are too generalized For varying scales, see data on these two BC online mapping websites: www.mapplace.ca or www.lrdw.ca Precision Precision is based on scale – how exactly can a coordinate be specified On printed maps, this was equivalent to ~ 0.5mm (= 25 metres at 1:50,000 … or 125 metres at 1:250,000) GIS software uses ‘double- precision’ giving up to 6 decimal places of meters In most cases, this is bogus as not warranted by the data quality Further reading on GIS basics: http://www.innovativegis.com/basis/ primer/primer.html Data formats File formats Stored in a variety of formats Maintain the same basic principles of “PLP” Lab work will focus on 2 formats common to ESRI products ◦ Shapefiles ◦ Coverage ◦ Personal and file geodatabases are another preferred data format for. We will look at this at a later date. Shapefile/Coverage Shapefiles (ESRI) Arcview .shp Spatial data e.g. rivers.shp .shx Index link file e.g. rivers.shx .dbf Attribute data e.g. rivers.dbf Also: .prj Projection file .sbn and .sbx .. optimise spatial queries http://en.wikipedia.org/wiki/Shapefile Coverage (ESRI) - Arc/Info Layer name folder e.g. roads (spatial) : 6-10 files Info folder (attributes): many files Multiple files per layer – zipped into one export .e00 format Other Data formats Computer assisted drafting formats: ◦ .dxf (Autocad) ◦ .dgn (Microstation) Raster formats: ◦ .tif ◦ GeoTIFF Full list for ESRI List of data formats supported by ArcGIS Many more can be converted with FME (Feature Manipulation Engine) from http://www.safe.com Managing files ArcCatalog is built specifically to manage GIS data Managing files using Windows has some inherent risks. Quick message Hello Terrace Amy Hillier. 2011. "Manual for working with ArcGIS 10" The Selected Works of Amy Hillier Available at: http://works.bepress.com/amy_hillier/24/ Georeferencing How do we make sure all our data layers line up ? Georeferencing: = linking a layer or dataset with spatial coordinates Registration: = lining up layers with each other Rectification: =The process by which the geometry of an image is made planimetric If the world was flat, we could use a simple coordinate system with 0,0 in the bottom left corner (or A1) … but alas it isn’t … The edge of the world … Geographic referencing 180 E/W PG: 54N, 123W [54, -123] Geographic referencing is suitable for storing global 0, 0 datasets, but involves negative values south and west of 0, 0 Geographic referencing Geographic is not decimal, it is sexagesimal 1 degree = 60 minutes 1 minute = 60 seconds Decimal degrees: 58° 30’ = 58.5 30/60 = 0.5 Decimal degrees: 58° 36’ = 58.6 36/60 = 0.6 Decimal degrees: 58°36’36” = 58.61 36/(60*60) = 0.01 View decimal degrees on pgmap website (use Internet Explorer / Active X) The main problem with geographic referencing (for GIS data display and analysis) - 1 degree longitude varies from 0 - 111 km (the system is not ‘rectangular’ ) Local example from the phone book 2007 (OK) –scale is consistent 2008: horizontal scale is almost double Length of One Degree of Longitude Length of a Degree of Latitude Latitude Kilometres Miles Latitude Kilometres Miles 0º 111.32 69.17 0º 110.57 68.71 10º 109.64 68.13 10º 110.61 68.73 20º 104.65 65.03 20º 110.70 68.79 30º 96.49 59.95 30º 110.85 68.88 40º 85.39 53.06 40º 111.04 68.99 50º 71.70 44.55 50º 111.23 69.12 60º 55.80 34.67 60º 111.41 69.23 70º 38.19 23.73 70º 111.56 69.32 80º 19.39 12.05 80º 111.66 69.38 90º 0.00 0.00 90º 111.69 69.40 1° Longitude is half the distance at 60N 1° Latitude = ~ 111km anywhere Earth is not a perfect sphere, it is ellipsoidal .. earth is the 'Geoid'. The difference in the major and minor axes has been estimated since ~1830 The latest should be the most accurate, using satellite technology. The difference representing the amount of 'polar flattening' is about 1/300 . Estimated ellipsoids Equatorial Polar Radius a Radius b Name Date Flattening (metres) (metres) WGS 84 1984 6,378,137 6,356,752 1/298 International 1924 6,378,388 6,356,912 1/297 Clarke 1866 6,378,206 6,356,584 1/295 Everest 1830 6,377,276 6,356,075 1/301 Each ellipsoid has a 'Datum' = "a set of values that serve as a base for mapping“. For Canadian / North America, we use: a. North American Datum, NAD27 (1927) based on Clarke 1866 b. North American Datum, NAD 83 (1983) based on WGS 1984 NAD27 was the datum for mapping over most of the 20th century NAD83 is the datum for contemporary GIS / mapping Universal Transverse Mercator (UTM) System this bit is hard so pay attention … The world is divided into 60 x 6 º longitude strips - the width of each zone thus varies from 6 x 111km = 666 km at the equator to < 80 km at 84 ° N They are numbered 1 - 60 from 180 º W to 180 º E 180W 180E Canada: UTM zones UTM coordinates – in metres - this is the hardest part … Northings (N): from the Equator – increase to the north (to 10,000,000) Eastings (E) – based on the zone Central Meridian at 500,000 Coordinates repeat for each zone In BC, eastings are usually between 300,000-700,000 UTM zone overlap: Topographic map with Geographic and UTM referencing UTM zone Eastings coordinates in BC are generally between 300,000 – 700,00 UTM coordinates may make more sense here : PGMAP: http://pgmap.princegeorge.ca/ (use Internet Explorer / Active X) The UTM system works well for a local area – coordinates in metres BC: UTM zones How do we deal with multiple UTM zones: Eastings coordinates switch from ~700,000 at the east edge of one zone to ~300,000 at the west edge of the next (= same place) Albers (conic) projection e.g. Yukon Albers: http://www.environmentyukon.gov.yk.ca/geomatics/techweb/yt-albers- projection.html BC Albers projection Central meridian: 126 W First Standard Parallel: 50N Second Standard Parallel: 58:30N Latitude of projection origin 45N False northing 0 False easting 1000000 (1million m) Summary: BC mapping coordinates BC geomatics industry ‘recognises’: 1. Geographic – latitude / longitude – for data storage 2. Universal Transverse Mercator (UTM): zones 7-11 - local / regional 3. BC Albers - for provincial data View all 3 on: http://www.lrdw.ca (imap) (use Internet Explorer-IE) [sometimes!] View Geographic and Albers on http://www.mapplace.ca (use IE / Active X) Multiple coordinate systems Georeferenced data can be recognised by the coordinates e.g. Prince George Geographic: -123 54 UTM zone 10: 512,000 5972,000 BC Albers: 1,200,000 1000,000 GIS software today can overlay these by projecting ‘on the fly’ Where these would plot if not properly defined: y UTM To be able to do analysis, layers MUST be reprojected into the same projection and datum e.g. UTM -> Albers NAD 27 -> NAD83 A G x http://earthobservatory.nasa.gov/IOTD/ Key points GIS falls under the umbrella of Geomatics GIS is an automated process GIS involves spatial locations 4 main components of a GIS are ◦ Acquisition (Input) ◦ Management ◦ Analysis ◦ Display (Output)
"gis_basics.pptx - UNBC GIS Remote Sensing Lab"