Introduction to GIS Theory Research Computing Services Sept. 10, 2021 Dennis Milechin, P.E. [email protected] Please fill out tutorial evaluation: http://rcs.bu.edu/eval Introduction to GIS Theory 9/10/2021 Housekeeping - This session is recorded. - Will be published here: https://www.bu.edu/tech/support/research/training-consulting/access-training-materials/ Link to Presentation: http://rcs.bu.edu/examples/gis/tutorials/gis_theory/intro_to_gis_theory.pdf 2 Introduction to GIS Theory 9/10/2021 Outline - What is GIS? - Datum - Geographic Coordinate System - Projections - Common Spatial Data Models - Data Layers - Spatial Data Storage - Example Workflow - Sample GIS Software 3 Introduction to GIS Theory 9/10/2021 What is GIS? - Most of us are familiar with tabular data. 4 Introduction to GIS Theory 9/10/2021 What is GIS? - Import tabular data into GIS. 5 Introduction to GIS Theory 9/10/2021 What is GIS? - Import tabular data into GIS. 6 Introduction to GIS Theory 9/10/2021 What is GIS? - Import tabular data into GIS. 7 Introduction to GIS Theory 9/10/2021 What is GIS? - Geographic Information System “A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present spatial or geographic data” https://en.wikipedia.org/wiki/Geographic_information_system 8 Introduction to GIS Theory 9/10/2021 What is GIS? - Typical functions of GIS software - Read/write spatial data - Maintain spatial meta data - Apply transformations for projections - Apply symbology based on attribute table - Allow layering of data - Tools to query/filter data - Spatial analysis tools - Exporting tools for printing maps or publish web maps 9 Introduction to GIS Theory 9/10/2021 Datum 10 Introduction to GIS Theory 9/10/2021 Datum - The earth is generally round, but is not a perfect sphere or very smooth (e.g. mountains and canyons) Source: https://en.wikipedia.org/wiki/Ellipsoid 11 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System (GCS) 12 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System - How do I tell a computer where we are located on earth? My office (42.350083 N, -71.104168 W) 13 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System Cartesian Coordinate System (50 E, 40 N) Point (2,2) Source: https://www.e-education.psu.edu/natureofgeoinfo/c2_p10.html GCS Source: http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/geographic-coordinate- system.htm Source: http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/about-geographic-coordinate-systems.htm 14 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System (+) (-) (+) (-) Units Short Hand Compass Example +/- Example Degrees Minutes dddº mm′ ss.s″ 45º 36′ 23″ N, 122º46′ 18.4″ W 45º 36′ 23″ , -122º46′ 18.4″ Seconds Degrees Decimal dddº mm.mmm′ 45º 36.38′ N, 122º 46.31′ W 45º 36.38′ , -122º 46.31′ Minutes Decimal Degrees ddd.ddddddº 45.6064º N 122.7718º W 45.6064º, -122.7718º Additional Reading: http://geokov.com/education/latitude-longitude.aspx 15 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System Decimal places and accuracy of position. Additional Reading: https://en.wikipedia.org/wiki/Decimal_degrees 16 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System - There are many GCSs. - They are updated occasionally. - North American Datum (NAD) - NAD 27 - NAD 83 (with 5 updates) - New Datum in 2022! List of GCS supported by ArcGIS: https://desktop.arcgis.com/en/arcmap/latest/map/projections/pdf/geographic_coordinate_sy Source: https://en.wikipedia.org/wiki/Ellipsoid stems.pdf 17 Introduction to GIS Theory 9/10/2021 Geographic Coordinate System NAD 1927 NAD 1983 Coordinates are associated with a specific GCS. Above is an outline of Boston City Hall. The same coordinates 18 were used to plot the outlines in two different GCSs. Introduction to GIS Theory 9/10/2021 Projections 19 Introduction to GIS Theory 9/10/2021 Projections Greenland What is wrong with this map? Country Area ( mi ^2) Africa 11,730,000 Antarctica 5,405,000 Greenland 836,300 Africa Antarctica 20 Introduction to GIS Theory 9/10/2021 Projections Source: https://www.youtube.com/watch?v=CPQZ7NcQ6YQ Additional Reading: https://laughingsquid.com/world-mercator-projection-map-country-size/ 21 Introduction to GIS Theory 9/10/2021 Projections - Allow creation of flat maps. - At expense of distorting: - Shape - Area - Direction - Distance - Coordinates are typically in feet, or meters, and positive values - e.g (114564 ft, 53746 ft) Fun Read: “America Has Two Feet. It’s About to Lose One of Them.” https://www.nytimes.com/2020/08/18/science/foot-surveying-metrology-dennis.html 22 Introduction to GIS Theory 9/10/2021 Projections Cylindrical Conical Planar 23 Source: https://docs.qgis.org/3.10/en/docs/gentle_gis_introduction/coordinate_reference_systems.html#id1 Introduction to GIS Theory 9/10/2021 Projections Tissot's Indicatrix Conformal Equal Area Equidistant Source and Additional Reading: 24 http://geokov.com/education/map-projection.aspx Introduction to GIS Theory 9/10/2021 Source and Additional Reading: Projections http://downloads2.esri.com/support/documentation/ao_/710Understanding_ Map_Projections.pdf 25 Introduction to GIS Theory 9/10/2021 Projections World Fuller Cube World Polar NSIDC EASE Grid North NAD 1983 UTM Zone26 15N Introduction to GIS Theory 9/10/2021 Projections Universal Transverse Mercator (UTM) source: https://gisgeography.com/utm-universal-transverse-mercator-projection/ Source: https://www.e-education.psu.edu/natureofgeoinfo/c2_p22.html UTM Zones for US source: https://gisgeography.com/utm-universal-transverse-mercator-projection/ Source and Additional Reading: https://www.e-education.psu.edu/natureofgeoinfo/c2_p22.html https://gisgeography.com/utm-universal-transverse-mercator-projection/ 27 Introduction to GIS Theory 9/10/2021 Projections Many GIS packages takes care of the math. Phew! - What projection/GCS do I choose? - Institutions or Organization may select a standard coordinate system. - Choose one that minimizes distortion characteristics important for your analysis. - When to select/change GCS or projections in GIS? - Importing raw data into GIS - Georeferencing images or old maps. - Importing CSV files NAD 1927 NAD 1983 - Spatial processing of two layers. - Some GIS tools expect projected data. 28 Introduction to GIS Theory 9/10/2021 Projections Types of Projection Definitions - EPSG - MapServer Mapfile | Python - Well Known Text as HTML - Mapnik XML | Python - Human-Readable OGC WKT - GeoServer - Proj (formerly proj4) - PostGIS spatial_ref_sys INSERT - OGC WKT statement - JSON - Proj4js format - GML - ESRI WKT - .PRJ File - USGS 29 Introduction to GIS Theory 9/10/2021 Projections Sample Projection Definitions for NAD83 / Massachusetts Mainland (ftUS) Definition Type Example EPSG 2249 Proj4 +proj=lcc +lat_1=42.68333333333333 +lat_2=41.71666666666667 +lat_0=41 +lon_0=-71.5 +x_0=200000.0001016002 +y_0=750000 +ellps=GRS80 +datum=NAD83 +to_meter=0.3048006096012192 +no_defs .prj PROJCS["NAD83 / Massachusetts Mainland (ftUS)",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",S PHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["De gree",0.017453292519943295]],PROJECTION["Lambert_Conformal_Conic"],PARAME TER["standard_parallel_1",42.68333333333333],PARAMETER["standard_parallel_2", 41.71666666666667],PARAMETER["latitude_of_origin",41],PARAMETER["central_me ridian",- 71.5],PARAMETER["false_easting",656166.667],PARAMETER["false_northing",24606 25],UNIT["Foot_US",0.30480060960121924]] 30 Introduction to GIS Theory 9/10/2021 Projections Sample Projection Definitions for NAD83 / Massachusetts Mainland (ftUS) Definition Type Example Well Known PROJCS["NAD83 / Massachusetts Mainland (ftUS)", GEOGCS["NAD83", Text (WKT) DATUM["North_American_Datum_1983", SPHEROID["GRS 1980",6378137,298.257222101, AUTHORITY["EPSG","7019"]], AUTHORITY["EPSG","6269"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4269"]], UNIT["US survey foot",0.3048006096012192, AUTHORITY["EPSG","9003"]], PROJECTION["Lambert_Conformal_Conic_2SP"], PARAMETER["standard_parallel_1",42.68333333333333], PARAMETER["standard_parallel_2",41.71666666666667], PARAMETER["latitude_of_origin",41], PARAMETER["central_meridian",-71.5], PARAMETER["false_easting",656166.667], PARAMETER["false_northing",2460625], AUTHORITY["EPSG","2249"], AXIS["X",EAST], AXIS["Y",NORTH]] 31 Introduction to GIS Theory 9/10/2021 Projections Additional Reading - http://geokov.com/education/map-projection.aspx - https://www.axismaps.com/guide/general/map-projections/ - https://alastaira.wordpress.com/2011/01/23/the-google-maps-bing- maps-spherical-mercator-projection/ - http://bl.ocks.org/syntagmatic/raw/ba569633d51ebec6ec6e/ Projected Coordinate Systems supported by ArcGIS Pro - https://desktop.arcgis.com/en/arcmap/latest/map/projections/pdf/project ed_coordinate_systems.pdf Projection Definition Lookup reference - https://spatialreference.org/ref/epsg/ 32 Introduction to GIS Theory 9/10/2021 Review 1. To plot spatial data we need Datum and Geographic Coordinate System (GCS). Source: http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/about-geographic-coordinate-systems.htm 2. Use GCS to assign coordinates to data. 40º 00′ 00″ N, 50º 00′ 00″ E Source: http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/geographic-coordinate-system.htm 3. To make a flat map, need to apply a projection. 14572818.92E,