Datums and Map Projections by 
GIS fundamentals : a first text on geographic information systems, 5th ed. by You will need to work with both vector data and raster data as you construct your final GIS maps for Maritime Archaeology.
Vector data is visually represented on a map as points, lines, or polygons. Our workshops will cover how to plot the x,y locations for your shipwreck's artifacts so they display as points on your map. We'll also cover how to search for supplemental vector data for your project such as:
Image source: National Ecological Observatory Network (NEON)
Raster data uses equal-sized cells (pixels) arranged in a grid to represent geographic data. Some common examples of raster data are aerial photos and satellite imagery, scanned maps, elevation models, etc. You'll integrate raster data into your project when you upload and georeference a scanned drawing of your shipwreck. We'll also discuss how to access satellite imagery and environmental data in raster format.
Image source: World Imagery Wayback
Datums are an essential component of every mapping project since they provide a standard reference point for measuring surface distances on the Earth. Horizontal datums provide an reference origin point (0,0) for latitude/longitude lines (in relation to a reference ellipsoid). Vertical datums provide a standard reference point (e.g., mean sea level) for measuring elevations .
When you are working on GIS projects, you will need to pay attention to the datum(s) of existing data sets since using data with different datums can impact your analysis and how your data lines up on your map. If you are working with data sets that are based off of different datums, you'll need to use some of the built-in tools in ArcGIS Pro to convert all of your data to a common datum.
The following resources provide a helpful overview of horizontal and vertical datums and why they're important for GIS:
A datum is one component of a coordinate reference system. A coordinate reference system helps GIS software like ArcGIS Pro interpret your data by telling the software where your data is located in the world and how to display your data on a flat surface like a map.
Geographic coordinate systems tell the software where in the world specific features are located via latitude / longitude coordinates. The measurement units are angular (e.g., degrees). Projected coordinate systems tell GIS software how to take the geographic coordinate information and represent it on a flat surface like a map using specific measurement units, directives for how to center the data, etc. The measurement units for projected coordinate systems are usually linear (e.g., meters). Since there's no way to flatten the Earth without some form of distortion, this is where map projections come into play.
Check out the following resources to get a quick intro to map projections and how to determine which map projection(s) are suitable for your study area and analyses.
The research team who mapped the wreck of the HMS Colossus used the Universal Transverse Mercator (UTM) system. The UTM system is a plane coordinate system based off of the Mercator projection. It divides the world into 60 zones that are 6-degrees of longitude wide. The UTM system provides coverage for the majority of the world, except for polar regions. The UTM system uses meters for its unit of measurement.
Measurements for the HMS Colossus are based on UTM Zone 30 and the WGS84 datum (World Geodetic System 1984).
Image source: Wikimedia Commons
