Creating a "heat map"
(class-break renderer)
The Visualization options of OCHRE's Map View include the ability to create "heat maps" (based on class-break renderers) to show the proportion of items of a specific type (classes of items), spatially situated on a map. To illustrate, consider the example from the ancient site of Ugarit (Ras Shamra) where the find-spots of Texts, by language, are shown in their relative proportions on a "heat map."
Texts, shown spatially, in relative proportions by language (Akkadian, Hurrian, Ugaritic).
Requirements
To create a "heat map" showing relative proportions of items of a specified type, OCHRE requires the following specifications.
A Set: Create an OCHRE Set that contains the items of interest, here a list of Text items tagged as to their Language (using a property for Language in the ordinary way). The Set needs to include a "group-by" property that organizes the items of the Set spatially into predefined groups; that is, there needs to be locational information (Coordinates, or Coordinate-property) inherent in the group-by selection. In this example, the "group-by" element (use the paperclip-asterisk button) is the topographical point that identifies Text items found in a particular location within the architectural framework at Ugarit.
Specifically, the network of information includes:
Text items that are associated with tablets (Spatial units) using the relational property "Associated text/item."
Those tablet items also have a relational property Topographic point which target other spatial items which have locational information representing find spots of tablets at the site of Ugarit.
The Topographic point items being referenced as the targets of the relational property Topographic point have spatial information, assigned using the Coordinate metadata of the spatial units. These coordinates represent the find spots of tablets at the site of Ugarit.
A Style: Create a Style for Map View that includes specifications for class-break intervals. From the Project, Preferences, Styles option, create a Style based on the Properties of the items to be grouped and counted on the "heat map" View. Here we are basing the view on the Language values of the implicated Text items, specifying different colors for each of the language options (the classes), and assigning class-break intervals to the parent property, here Textual feature, that manages the classes.
Class-break intervals
A Class of "1-20-1000" will specify 3 classes based on counts of instances of items that fall within: 0 - 1 instances; 2 - 20 instances; and 21 - 1000 instances. A class of 5-10-1000 will specify 3 classes based on counts of instances of items that fall within: 0 - 5 instances; 6 - 10 instances; 11 - 1000 instances. [Note that "1000" represents a generic upper limit, not intended to represent real data but to give a outer limit to the range of the uppermost class specified.]
For each "class," OCHRE will specify a progressively larger circle to indicate the proportion of items that fall within that class. The circles will be colored based on the colors assigned to the classes in the Style selected for the View.
A shapefile: Link a proto-shapefile to the "Contextual geodatabase or shapefile" of the Map Options of the Query Inbox of the project, in order to identify the spatial reference of the Map. OCHRE will use the .prj file of this shapefile as a display directive. Any shapefile that includes an appropriate projection (.prj) will be sufficient here.
Map View, as Class-break renderer
From OCHRE's Map View, select the Style (be sure to select this in advance using the bow-tie button on the right-most Map View toolbar) that references a class-break renderer specification. This will give you the option to view the Set in a Class-break View. OCHRE will use the intervals specified by the class-break of the selected Style to show the items of the Set classified according to the proportions determined by the group-by elements of the Set.
Once the above initialization is in place, you can toggle on a Set in OCHRE's Map View by checking ON its checkbox.
(If you choose not to view the Set using its class-break renderer, the items will be plotted on the Map View in the usual way.)
Colors from the chosen Style will be derived for the View.
The circles on the "heat map" are drawn in lighter to darker colors, representing the scale of the designated class breaks. For example, if an Gray color is chosen for a Property-based specification (e.g. Texts of Akkadian = Gray), then a lighter color (Light Gray) will be used for quantities at the low end of the class-break scale (0 - 5), and a darker color (Dark Gray) will be used to represent quantities of Akkadian texts at the higher end of the class break scale (101 - 1000).
The circles are drawn in smaller to larger sizes, representing the proportions of items of each class associated with the find spots.
In this example, OCHRE follows the links from the Texts (broken out by Language) -- to the tablets -- to their find-spots (Topographic points) and counts the number of texts of each class (language) at each find-spot location, drawing a circle there of the appropriate color and size.
