Digitising archaeological data

Having collected all this data we want to show you what can be done with it. We are going to digitise and combine the archaeological information that all these different sources contain – new skills for this course.

Lake Hamrin sites

For our case study, we are going to draw boundaries for the Lake Hamrin sites that we can identify, add name data from the maps if they are available, and record whether or not they are covered by the reservoir in the 1990 Landsat and 2022 Sentinel imagery. This will help identify which sites are most at risk from erosion.

Creating a shapefile

The first thing we need is a file to store this archaeological data in. As we want to record specific features we will need to create vector data (Week 1.10). There are different file types we could use, but we are going to use a shapefile as they are widely compatible across different GIS programs.

• 1) On the Menu navigate to “Layer” > “Create Layer” > “New Shapefile Layer…”
• 2) Click the browse button and give your shapefile a name and save it into a suitable location. We have created an “Archaeology” folder inside our Lake Hamrin directory.
• 3) For “Geometry type” select “Polygon”. If you want point or line features, select these instead.
• 4) Select “WGS 84” for the coordinate reference system (unless you want to use a local grid).

We then have to list the fields that we want in our shapefile’s attribute table – the data we want to record for the sites. We are going to start with three fields to record the name of the site, and whether it is flooded in the 1990 and 2022 imagery. Your fields will obviously look different depending on what you want to record: perhaps the type of site; the number of features forming the site; or the main threat to the site.

_{What fields will you need to record the archaeology in your area?/sub>}

• 5) In the “New Field” box type “site_name” for name.
• 6) Make sure “Text” is selected – as we want to type in our name using letters.
• 7) Make sure the “Field Length” (the number of letters allowed) is long enough, in our case 80 is fine.
• 8) Click the “Add to Field List” button.

_{Creating our new shapefile.}

_{You should see that there is already an “ID” field in the field list. This is an integer field, which means it will only accept whole numbers – no letters or decimal points. This is a good field to use for uniquely identifying new sites without a name. We are going to use it for the site number from our map. If you don’t want it, you can remove it by selecting it and clicking the “Remove Field” button.}

We are going to repeat this process for two more text fields: “flood_1990” and “flood_2022”.

• 9) Once you are happy with your fields, click OK.

_{Adding all the fields, you can remove the “id” field if it is not useful.}

Your new polygon shapefile will be added to your Layers Panel, but we haven’t added any sites yet so you won’t see anything in your Map Window.

_{The new shapefile has been added to the Layers Panel.}

Creating new features

Now that we have a file to store the data in we are going to digitise some sites!

• 1) Right-click your shapefile in the Layers Panel and click “Toggle Editing”.

In GIS software “editing” is a common safeguard to prevent you making changes to your data by mistake, we turn editing on for each file we want to change, save our edits as we go along, and then stop editing when we have finished.

• 2) Find a site you want to digitise in the Map Window.

We are going to start with Sabra (site 66), a small tell in the middle of our map. It is visible on the Corona and Sentinel-2 imagery, but it is flooded in the 1990 Landsat.

_{Sabra is visible on the Corona imagery, the archaeology map (McGuire 1981), and the Sentinel-2 imagery, but is flooded in the 1990 Landsat. Imagery courtesy of the USGS and ESA.}

• 3) When you are ready to draw the boundaries for your site, click the “Add Polygon Feature” button.
• 4) Left-click to add vertices to your polygon and right-click to finish drawing it.

_{Left-click to draw around your site and right-click to finish.}

• 5) Add the attributes for your site when the window pops up and then click OK.

_{Add information for your site in the Feature Attributes window that pops up.}

Viewing and editing feature attributes

If you want to have a look at or edit the data you have already collected, you can see it in the attribute table.

• 1) Right-click your shapefile in the Layers Panel and select “Open Attribute Table”.

_{The attribute table shows you all the data you have collected, selected sites will be highlighted in yellow.}

If you click the row number for each feature it will be highlighted in yellow in the Map Window. If you want to alter any of the information you have added, you can do this in the attribute table.

• 2) Make sure editing is turned on for the feature, if it isn’t you can click the yellow pencil button in the top-left of the attribute table.
• 3) Click on the text or number you want to change.
• 4) Change the value.
• 5) Save your edits by clicking the “Save Edits” button.

_{Editing site attributes.}

Adding extra fields

If you decide you need an extra field to record more information about your site, you can do this from the attribute table.

• 1) Open the attribute table and turn on editing.
• 2) Click the “New Field” button.
• 3) Provide the name, type and length of your new field and click OK.

_{Adding a new field.}

• 4) Add in the missing data for your new field in the attribute table.
• 5) Save your edits and turn off editing.

_{Adding the missing data to our new field.}

Once we have collected all our data, we will want to make some great maps to display it!