We are creating a map of trees, there are hundreds of millions of trees. We are representing each tree as a 'perfect circle' - as a polygon. We have two classes of tree in a single file geodatabase layer. The layer has the following attributes: tree height, canopy perimeter, canopy area (amongst others). The problem is that the polygon file is very large, the map is to go on ArcGIS online. We tried to recreate the same visual experience using Points rather than Polygons. The point layer carries identical information to the polygon layer. The difficulty is in the Symbology. Our points are drawn as circles, their Area is proportional to the Canopy Area, and this works. However, we have 2 classes of tree, and use two colours, one for each class. In the Symbology tool, it doesn't seem to be possible to assign more than one specific colour, so we cannot differentiate between the two classes as long as they are in the same layer. We can create two separate layers, but then we cannot control the rendering order. We want the tallest trees to render on top. Secondly, we could assign Unique Values, for the circle diamter, or circle area, or circle perimeter, but it is not possible to assign real units (metres), the units are fixed as pt. We followed this example here Display "Quantity by Category" Symbology in ArcGIS Pro but it is not helpful. Two questions: 1. Is it possible to assign real units to Unique Values? 2. Is it possible to assign specific colours to multiple classes in a single layer, when assigning Propportional Symbology?
# symbology code on arcade
var cls = DefaultValue(Text($feature.Class), "Unknown"); // FT / TOF
var h = $feature.Max; // meters
var hbin = When(
IsEmpty(h), "No height",
h < 5, "<5 m",
h < 10, "5–9.9 m",
h < 20, "10–19.9 m",
h < 30, "20–29.9 m",
"30+ m"
);
return cls + " | " + hbin;
See the last map (Trees by Canopy size and height) on the site Waterford City and County National Tree Map
