This is the second part in a two-part series on ArcGIS Pro for cultural heritage research. You can find Part 1 here.
In Part 2, this tutorial will cover tasks common in cultural heritage research including georeferencing scanned maps or drawings, tracing drawings to create lines and polygons within ArcGIS Pro, basic analyses, and producing maps for publication or presentation.
Working with raster images
Raster images are pixel based graphics and a frequent source of information. Scans of print maps, as well as scans of plan or drawings from the field are commonly brought into ArcGIS Pro to add data and information from different sources.
Similar to in Part 1, you will want to store the original raster images in a raw data (or whatever naming convention you decided on) folder and only work with copies. We recommend grouping data within this folder by the source.
Example: Geology map of Rebun Island, Japan
Steps
- Create a new folder in RawData called “ExternalSources” and then an appropriately named folder within that – in this case we’re going to bring in a geology map from an article by Yoshihiko Goto and Jocelyn McPhie so we’ll call the folder “Goto_McPhie1998”
- Add the raster image (rebun_geo.png) to this folder
- Create a new working folder in Working called “GeologyMap” and copy the png file here
- Open ArcGIS Pro and make sure the Catalog pane is open on the right side
- Navigate to the Working folder and drag and drop the “rebun_geo.png” onto your map
- A window will pop up asking if you want to calculate statistics for the file – click Yes
- The image will now be placed on your map and if you right click on the image layer in the Contents pane on the left side and select Zoom to layer it will show you where it was placed…which will be a random spot. In order to have the image placed correctly on the map, you will need to “georeference” it!
Georeferencing
Georeferencing allows you to locate raster data (i.e. scanned images or documents) to a map coordinate system aka tagging parts of the image to specific coordinates. Depending on the spatial accuracy of the image, you may be able to easily register it within your map or you may end up with a warped version of the image (especially with historic maps or drawings that were done without precise instruments).
Typically you want to find at least 3-4 spots on the image that you either have GPS points for or can locate on the basemap. They should be well distributed across the image (i.e. for a square image close to the four outer corners).
Steps
- Search for “Georeference” in the Command Search at the top center of the menu bar
- This will open the Georeference tab in the Ribbon along the top, towards the left side. If you click on the button Fit to Display it will resize and place the raster image you have selected to your current map view. This can be extremely handy – zoom to the area that maps to your raster image and then click on Fit to Display.
- In order to assign coordinates to the raster image, you will add “control points” – these are tagging specific places on the raster image with absolute coordinates. Click on the button Add Control Points and your cursor will change to a small plus sign. Now the first time you click, you will be adding a “source” point (aka selecting a place on the raster image) and the second time you click, you are adding a “target” point (aka the coordinate location on the map that is associated with the source point).
- Add 3-4 control points that are well distributed, ideally around the edges of the raster image.
- You can toggle the raster image on and off using the checkbox to the left of the raster layer in the Contents pane to navigate between the map view and the raster image. Alternatively, you can change the transparency of the raster by opening the Raster Layer tab in the ribbon and then adjusting the transparency (typically between 40 – 60% works best).
- Having Auto Apply toggled on (highlighted blue in the Adjust section of the Georeference tab) the raster image will automatically adjust to fit the control points as you add them.
- Once you have the raster image adjusted as desired, click on Save in the Georeference tab to lock in those control points and save the now georeferenced raster image. Click on Close Georeference.
Tracing
In some cases, you may want to trace sections of a raster image that has been georeferenced (i.e. adding polygons from a geology map or contour lines from a topographic map). If you are comfortable with a vector software application, you can trace the lines in that application and then bring the vector art into ArcGIS Pro and georeference it just like you did with the raster image. However, you can also trace directly within ArcGIS Pro and it has some handy features to speed up the process.
Steps
- In the Catalog pane, right click on the folder with the working files associated with the map you are creating and select New >> Shapefile
- Give the shapefile an appropriate name and select the desired type (i.e. polygon or line)
- Assign the shapefile to the same coordinate system as the current map and then click Run
- The shapefile will be added to the map as a new layer in the Contents pane on the left side
- Click on the Edit tab along the top and then select the new layer from the Create Features pane that opens on the right
- The first icon in the list that appears will allow you to create a new Polygon or Polyline, click on this and then navigate to the map
- NOTE: you can hold down the C key to temporarily change your cursor to the “Explore” tool which will allow you to pan and move around the map without adding points
- Trace the feature you are interested in and once finished, doubleclick to complete the polygon or line
- If desired, you can open the Attribute table and add any values to the fields of the newly created polygon or line
If you are tracing features that overlap, ArcGIS Pro allows you to easily select and recreate portions of polygons or lines that you’ve already created by using the Trace tool
Steps
- In the Create Features pane on the right, select the Trace tool
- Drag your cursor along the section of the polygon or line that you want to duplicate and you’ll see a faint grey line marking what will be copied. Click on the map to end the tracing session and then select the Polygon or Polyline tool again to add points that are not part of a previously created polygon or line
Recommendation: periodically click on the Save button in the Edit tab so you don’t lose any of your tracing work!
Analyses
Common analyses used in cultural heritage research include the following:
- Cost Path – what route from point A to point B requires the least “cost” or effort if factoring in elevation changes (or other factors)
- Line of Sight – indicates what is visible from a single vantage point when taking into account elevation and features that may block visibility
- Viewshed – displays visibility across a selected area
- Cluster analyses – identifying statistically significant areas of similarity
- Overview of different types of cluster analysis available in ArcGIS Pro
- Selected types
- Density-based clustering – cluster based on spatial distribution
- Hot Spot analysis – find hot spots based on weighted features
- Multivariate clustering – cluster based on attributes
- Similarity search – find features that are most similar to the attributes of a selected feature
- Centroid – calculate a point feature at the center of a polygon feature
- Contours – creating contour lines from raster or elevation data
- Spatial relationships modeling – using spatial patterns to model and predict
- Colocation analysis – measure local patterns of spatial associations based on two categories
- Generalized Linear Regression – generate predictions by modeling relationships between variables
- Generate Spatial Weights Matrix – generate representations of spatial relationships that can be used with various tools
- Spatial Association between Zones – measure the degree of association between different zones based on spatial overlap (useful for comparisons over time)
Producing maps for publication and presentations
Once you have your map with all of the data and styling established, you will probably want to prepare a version that can be used in publications and/or presentations. This is achieved through “layouts” in ArcGIS Pro. In each layout, you can add a north arrow, scale bar, legend and text (along with other graphics such as charts or an attribute table). For many of these, styling them takes digging through various menus and panes so we recommend saving styles so you can reuse them across layouts.
Steps
- Open the Insert tab and click on New Layout then select the most appropriate page size
- A new layout will be created in the Layouts folder and you can rename it by double clicking on the layout layer in the Content pane. Switch to the General tab and then change the name
- In the Insert tab on the ribbon, click on Map Frame and then select the map that you would like to add to the layout – drag a box on the page and the map will fill this box
- In order to adjust the zoom or view of the map within the frame, you need to “activate” it first – switch to the Layout tab in the ribbon and click on Activate, then you will be able to maneuver the map. Once finished, click on the Layout tab in the ribbon and select Close Activation
- Add graphics such as a north arrow, scale bar, and legend through the Insert tab
- Each of these can be styled by double clicking on the graphic in the map and then navigating through the settings on the Element pane that will open on the right side
- Once you have styled as desired, select the graphic on the map, then right click on it and select Save to Style. This will allow you to reuse the styled element without needing to go through all of the settings again.
- Once you have the layout finalized, open the Share tab in the ribbon and click on Export Layout – select the desired format and adjust the settings in the export pane as desired