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Class-Specific Resources

GIS Data Viz: Drawing by Hand

Content

  • Creating New Layers
  • Dropping Points
  • Drawing Lines

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.

 

STEP 1: Creating New Layers

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.

  1. In the top menu, go to Layer > Create Layer > New Shapefile Layer. For file name, click the box with three periods all the way to right, select a folder you want to store the new file in, and then give your file the name "Equiano-ports."

Creating a new shapefile layer

  1. For Geometry type, select Point.
  2. Now under the New Field section, let's add a field for the city name. Just type "city" into the Name field and then click "Add to Fields List. (Creating a new field adds a column to the attribute table for this dataset. If you wanted to, you could add many more fields. Type refers to the type of data you'll be storing in the field [i.e. text characters, integers, etc.]. And length is simply the maximum length of characters or digits that field should accept.)
  3. Now hit OK. You should see your new layer in the side panel, though there will be no points visible yet.
  4. Repeat these steps to create another point layer called "Hall-ports."

Next we'll add layers for our line data.

  1. Once again go to Layer > Create Layer > New Shapefile Layer. For file name, click the box with three periods all the way to right, select a folder you want to store the new file in, and then give your file the name "Equiano-journey."
  2. For Geometry type, select Line.
  3. Now hit OK. You should see your new layer in the side panel, though there will be no lines visible yet.
  4. Repeat these steps to create another line layer called "Hall-journey."

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.

STEP 2: Dropping Points

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.

  1. First make sure the "Equiano-ports" layer is selected. Then in the top menu, go to Layer > Toggle Editing—you can click on the Layer menu again to make sure this now has a check beside it. This allows you to edit this layer. (Note: you can also toggle editing on and off by clicking the single pencil icon in the menu bar.)

Toggle Layers

 

  1. Next, in the second row of menu icons, you should see an icon with three blue dots and a yellow boxed star (it should be two icons to the right of the yellow pencil icon). When you hover over it, it should "Add Point Feature."  Select that. In order to make it active on your map, you'll have to press control+. (command+. on Macs). Now you should see a kind of bullseye for your mouse when you hover on the map.
  2. With your bulleyes, find where you want to drop your first point—for Bight of Benin—and click. (Don't worry if you don't know exactly where to click. We can fix the location in a moment.) 
  3. When you click, you should see a popup. Give your point an ID number (it could be the port_id from the spreadsheet—60599) and type in the city name, which you may recall is the field we added when we created the layer. (Note that in this case, and in other cases, since we don’t know the exact name of the port, we’re using the name of the general region.) Click OK.
  4. To edit the location, select the tool that is next to the "Add Point Feature" tool. When you hover over it, it should say "Vertex Tool."
  5. Now hover over one of the points you just created. You should see a red outline appear around the point. Right click on the point. A "Vertex Editor" window should appear somewhere to the left of your screen.
  6. The vertex editor shows the point you just selected, specifically its x (longitude) and y (latitude) coordinates. You can highlight one or both of these and input or paste the exact coordinate you want and then hit enter. Consult the spreadsheet for the longitude (x) and latitude (y) values. Your point will move on the map to where you've now specified.
  7. Repeat steps 2–7 to add all of the points for Equiano.
  8. When you've added all the points, find the icon to the left of "Add Point Feature." When you hover over it, it should say "Save Layer Edits." Click this. Then click Toggle Editing in the Layer menu or the single pencil icon to turn off editing mode for this layer.

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.

Assigning Labels

  1. Double click the "Equiano-ports" layer and go to the Labels tab.
  2. Select "Single Labels from the dropdown menu. Then for Value select "city."
  3. Hit Apply.
  4. Now select the Symbology tab. Adjust the color of the points for this layer however you see fit.
  5. Hit Apply and OK. Then repeat these steps for the "Hall-ports" layer selecting a different color for the points in that layer.

STEP 3: Drawing Lines

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

  1. Select the "Equiano-journey" layer.
  2. Make sure that edit mode is toggled on. You can check by selecting  Layer in the top menu.
  3. In the same row of icons you were working before, you should now see in place of the "Add Point Feature" an icon with a connected line called "Add Line Feature." Click that.
  4. With this tool you can draw a line on the map. Regular clicking will start the line or drop a new point in the line (for instance, if you want to draw a line in multiple segments that changes directions). When you are done drawing the line, right click. (If you have made a mistake prior to right clicking, press the escape key to clear your line and start over. If you've already right clicked, just hit cancel in the popup box.) Find the first port in Equiano's journey and start your line there, then move to the next port and click there. Then right click to close that line. Click ok in the popup (you do not need to add an ID).
  5. Use the same procedure to add a new line from port 2 to port 3. Then lines to connect the other stops.
  6. When you've add all the lines you want to add, save your edits.

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.

  1. Double click the "Equiano-journey" layer and select the Symbology tab.
  2. Look at the Symbol window and find the arrow symbol. Select it.

Selecting the Arrow Symbol

  1. Now near the top, find the "Simple fill" box, click it, and select a dark red color for the arrow.
  2. Hit Apply and OK. Repeat this process for "Hall-journey" and select a green color for the arrow.

Arrows connecting

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.