class: title-slide, center, middle # Computer Aided Archaeology ## 08 - GIS I ### Martin Hinz #### Institut für Archäologische Wissenschaften, Universität Bern 08/11/23 --- class:center,middle # Why Do We Create Maps? --- class:center,middle ## Types of Maps --- ## General Reference Maps -- + Show important physical features of an area -- + Include natural and man-made features -- + Usually meant to help aid in the navigation or discovery of locations -- + Usually fairly simple -- + Can be stylized based on the intended audience (tourists vs locals) --- class:center,middle  #####Source: https://map.schweizmobil.ch/ --- ## Thematic Maps -- + Focuses on a specific theme or subject area -- + Features on the map represent the phenomenon being mapped -- + Spatial features used for reference --- class:center,middle ## Distribution Map  .caption[Source: Steuer 1998] --- class:center,middle ## "Cultural" Map  .caption[Terberger et al. 2014] --- class:center,middle ## "Genetic" Map  .caption[Kayser et al. 2005] --- class:center,middle,inverse # Basic Map Elements --- class:center,middle ## Points  .caption[http://docs.qgis.org/2.8/en/docs/gentle_gis_introduction/vector_data.html#overview] --- class:center,middle ## Lines  .caption[http://docs.qgis.org/2.8/en/docs/gentle_gis_introduction/vector_data.html#overview] --- class:center,middle ## Polygons  .caption[http://docs.qgis.org/2.8/en/docs/gentle_gis_introduction/vector_data.html#overview] --- class:center,middle # How do we make maps? --- ## GIS [1] .pull-left[ > A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present spatial or geographic data. - Wikipedia ] .pull-right[  ] ### Or more simply > In a GIS, you connect _**data**_ with _**geography**_. [GISgeography.com](http://gisgeography.com/what-gis-geographic-information-systems/) --- ## Geographic Information Systems (GIS) -- + Create interactive queries (user-created searches) -- + Analyze spatial information -- + Edit data in maps -- + Present the results of all these operations .right[  ] --- ## What can we do with a GIS?  --- ## GIS is relevant .pull-left[ It might become your job, or at least an important part of it... ] .pull-right[  ] --- ## QGIS - a free and open source GIS software - https://www.qgis.org/ - If you not have already installed QGIS, please do now! .center[  ] .right[  ] --- ## Layers  #### Image Source: http://www.geocontrolling.com/co-je-gis.htm --- ## Raster vs. Vector .pull-left[  ] .pull-right[  ] --- ## Raster (files) -- .pull-left[ + essentially an image with geographic information, which is georefenced + mostly used for background maps + can also contain continouus spatial information (altitude, precipitation, site density, ...) + Multiple formats are available (.img, .grid, .tiff, ...) + GeoTiffs are a quasi standard ] -- .pull-right[  ] --- ## Shapefiles -- + Basic file for storing map elements -- + Stores spatial data, like points, lines, and polygons -- + Multiple files comprise a "shapefile" --  --- ## Shapefiles  -- + .shp—The main file that stores the feature geometry -- + .dbf—The dBASE table that stores the attribute information of features --- ## Shapefiles  + .prj—The file that stores the coordinate system information -- + .shx—The index file that stores the index of the feature geometry --- ## You might also see -- + .cpg—Identifies the character set to be used -- + .sbn and .sbx—The files that store the spatial index of the features --- ## Shapefiles + Have a few limitations -- + One geometry type (Point, Line, Polygon) per shapefile -- + So sometimes you end up with this:  --- ## Coordinates .pull-left[ Lat/long system measures angles on spherical surfaces * 60º east of PM * 55º north of equator * Lat/long values are NOT Cartesian (X, Y) coordinates * constant angular deviations do not have constant distance deviations * 1° of longitude at the equator ≠ 1° of longitude near the poles A basic Coordinate Reference System ] .pull-right[  ] --- class:center,middle # So what is a Coordinate Reference System? --- ## Projections -- + No one's favorite part of GIS -- + But a necessary part of it nonetheless -- + Convert points on the 3-dimensional Earth (**latitude** and **longitude**) to x and y coordinates on a 2-dimensional map --  [Digital Coast Geozone](https://geozoneblog.wordpress.com/2012/05/22/happy-birthday-mercator/) --- ## Coordinate Reference Systems .pull-left[ - Features on spherical surfaces are not easy to measure - Features on planes are easy to measure and calculate - distance - angle - area - Coordinate systems provide a measurement framework ] .pull-right[  ] --- ## Coordinate Systems and Projection [1] .pull-left[  ] .pull-right[  ] --- ## Coordinate Systems and Projection [2] .pull-left[ - an imaginary light is “projected” onto a “developable surface” - a variety of different projection models exist - Map projections always introduce error and distortion ] .pull-right[  ] --- ## Projections + Every projection distorts some part of your map  [FlowingData](http://flowingdata.com/2014/01/13/map-projections-illustrated-with-a-face/) --- ## Projections Matter -- + These circles are all the same size on the globe:  [Progonos](http://www.progonos.com/furuti/MapProj/Normal/CartProp/Distort/distort.html) --- ## Projections Matter + As are these:  [Progonos](http://www.progonos.com/furuti/MapProj/Normal/CartProp/Distort/distort.html) --- ## Projections Matter + And these:  [Progonos](http://www.progonos.com/furuti/MapProj/Normal/CartProp/Distort/distort.html) --- ## Projections Matter  --- ## Mercator Projections -- + A common map projection -- + Makes geometries near poles look bigger than geometries near the equator --  --- ## UTM .pull-left[ Universal Transverse Mercator (UTM) - Based on the Transverse Mercator projection - 60 zones (each 6° wide) - false eastings - Y-0 set at south pole or equator ] .pull-right[  ] --- ## Schweizer Landeskoordinaten .pull-left[ - a geographic coordinate system used in Switzerland for maps and surveying by the Swiss Federal Office of Topography (Swisstopo) - The map projection used is Oblique Mercator on an 1841 Bessel ellipsoid. - All coordinates are always positive, since Switzerland is located in the 1st quadrant of the coordinate system. ] .pull-right[  ] --- ## Datums and Ellipsoids .pull-left[ - The earth is essentially a potatoe... - Ellipsoids are geometric estimations of the shape of the earth with more or less accurary - a datum is a system that allows us to place a coordinate system on the earth’s surface based on a specific ellipsoid - examples: - WGS84 (Lat/Lng, UTM) - Bessel 1841 (Schweizer Landeskoordinaten) ] .pull-right[  ] --- ## Projections + Identified by unique IDs (**EPSG**) that make it easier to talk about them + EPSG: European Petroleum Survey Group Geodesy (it was introduced, because Oil companies were annoyed by the incredible number of different systems) -- + WGS 84 is referred to as **EPSG:4326** -- + Google Maps and other online sources often uses WGS 84 / Pseudo-Mercator (**EPSG:3857**) -- + CHTRS95 is referred to as **EPSG:2056** -- ## Remember these three and you should be set --- ## Georeferencing .pull-left[ The process of orienting a image in geographical space * Every map comes with its own projection. Sometimes known, more often not * Every mapping results in errors or imprecision. Every digitalisation adds errors up to that. * Scale matters: digitised information on large scale might be precise enough, on small scale not. It is necessary to keep meta-data to know how the data were digitised (on what scale) to be able to understand on what scale they might be used. ] .pull-right[   ] --- ## Digitising .pull-left[ The process of attaching geocoordinates to points on georeferenced maps Rather straight forward: * You have a layer of a certain geometry * You make it editable * You click on the feature of the scanned map * You specify additional information for that point * Rinse and repeat * Finally, save the layer ] .pull-right[  ] --- class: inverse, middle, center # Any questions? .footnote[ .right[ .tiny[ You might find the course material (including the presentations) at https://berncodalab.github.io/caa You can contact me at <a href="mailto:martin.hinz@iaw.unibe.ch">martin.hinz@iaw.unibe.ch</a> * Steiniger 2009, Free and Open Source Desktop GIS Projects and Software * Briggs 2019, GIS Fundamentals * Leeds, Raster GIS * Lawler/Schiess 2010, Projections and Coordinate Systems ] ] ]