GIS Data Viz: Drawing by Hand
Up until now, we have been working with data downloaded from slavevoyages.org, but what should you do if you want to map something that is not in this database or if you only want to work with a small piece of the website’s information? In these instances, you might consider plotting points or drawing lines by hand. Fortunately, QGIS makes this process fairly easy.
We'll practice how to draw points and lines by mapping the journeys of Equiano and Florence Hall. You can access a spreadsheet that lists all of the ports included in these journey's here. It contains ports where they embarked/disembarked, a unique id for each port, and region and coordinates of each port. We garnered the port names from Equiano and Hall’s diaries, and the coordinates from the original spreadsheet shared by the Slave Voyages team. If you didn’t have the original spreadsheet or if the ports were not listed on it, you’d have to look of the coordinates elsewhere or make an estimate.
This shortened spreadsheet will come in handy when we start dropping points on the map. But first we'll need to create new data layers for each of the datasets we'll be creating.
Start by creating a new project in QGIS called "Equiano-and-Hall." Since we'll be creating multiple new files, it's probably best to create a new folder within the folder you've been storing your GIS files in. You can name that folder Equiano-and-Hall as well and save your new project there. Now load in the basemap we've used for the past tutorials. Next you'll need to create new layers for the points and lines you'll be drawing. We'll start with the point layers.
Next we'll add layers for our line data.
When you've completed these steps, you will have created four new empty data layers in your project, but you won't see any data on your map until you start drawing points and lines.
Now we're ready to do some drawing. We'll start by dropping points. Take a look at the spreadsheet you just downloaded. It contains a list of ports that appear in the journey of Equiano and Hall respectively. These are the points we'll be adding to the map. We'll start with Equiano.
Repeat this process to add Hall's ports. Start by selecting the "Hall-ports" layer and toggling edit mode on for that layer. Then proceed through the steps as before. Remember to save your edits when you're done. When you've added all the points you need to add, you can toggle edit mode off.
Now before we proceed, it will be helpful to turn on the labels for the points we just dropped and assign different colors to the points for Equiano and for Hall.
Now let's draw lines to connect the ports we've added to the map. These lines will represent how these individuals moved along their journey from one port to the next. We'll start again with Equiano. Here's the journey we'll be following:
Bight of Benin, port unspecified >> Barbados (port unspecified) >> Virginia (port unspecified) >> London >> Montserrat (port unspecified) >> London
You can use this same procedure to add the one line needed for Hall's journey. Just remember to select the "Hall-journey" layer before you proceed. Here are the ports you'll need to connect for Hall:
Bight of Biafra and Gulf of Guinea Islands, port unspecified >> Port Royal, Jamaica
When your done adding the line for Hall's journey, save your edits and then select Layer > Toggle Editing to turn editing mode off. As with the point layers, you can click on each of these line layers and select the Symbology tab to change the color or style of line.
Your connecting lines now appear as arrows and do a better job at communicating movement. The default format of the QGIS arrows might seem a bit gaudy, so feel free to go back to Symbology and play around with things like fill color and size of the lines.
One final note about the new data you've created: The QGIS project is what brings your data together on a single map, but you've actually created four new datasets that you have been saved to your machine as Shapefiles. Shapefile is simply a file format for saving GIS data (GeoJSON is another). Shapefiles will appear in the folder you save them as not one but six related files. They will all have the same name but different file extensions, one of which will be .shp. Make sure you keep these files together—QGIS will need to see them all in the same folder to be able to load that file again in the future.