Visual Essay Map Layer Tag

The map shown for an active element can be augmented with one or more layers. Two types of layers are currently supported.

Syntax

<param ve-map-layer>

Options

• type: mapwarper or geojson. Defines the specific layer type.
• title: The title attribute serves a couple purposes for map layers. First, it is used a the label on map controls that enable/disable MapWarper layers and control the layer opacity. When the layer type is geojson the title, when provided, will override any predefined labels in the GeoJSON file when displaying location labels on a map. Note that when multiple features (and labels) are defined in a single GeoJSON file the title value will be used once for the aggregate features.
• url: URL to a GeoJSON file. This attribute is only used when the layer type is geojson. This can be a relative URL (for example, geojson/portugal.json) if the geojson file is located in the same Github repository as the essay. If not, the URL must be absolute.
• mapwarper-id: Defines the overlay ID when the layer type is mapwarper
• active: One of true (default if attribute is not provided) or false. This attribute defines whether the layer is activated on the map when initially displayed. In either case the user can toggle individual layers on/off using controls on the map.

The following options are to use the Leaflet Heatmap Layer Plugin to add a heatmap overlay on a map:

• heatmap - required
• url - required URL to dataset file, currently assumes this is a TSV tile.
• radius - optional (integer, default 15) Defines the radius of your datapoints. If scaleRadius is false, radius is measured in pixels. If scaleRadius is true it's measured in the scale of the map
• max-opacity - optional (float, default 0.6)
• scale-radius - optional (boolean, default false) Defines whether the radius should be scaled to accordingly to zoom level.
• use-local-extrema - optional (boolean, default false) Defines whether the heatmap should use a global extrema set via setData/addData OR a local extrema (the maximum and minimum of the currently displayed viewport)
• max - optional (integer, default 10) Sets the upper bound of your dataset

Usage Examples

<param ve-map center="32.262084, 64.391554" zoom="2.5" stroke-width="0" show-labels>
<param ve-map-layer geojson url="/geojson/peony.json" title="Peony Distribution" active> 

---

<param ve-map center="0.040297, -71.224280" zoom="3.8" marker-type="circle" stroke-width="0" fill-opacity="1">
<param ve-map-layer geojson active title="Aurea" url="https://jstor-labs.github.io/plant-humanities/data/heliconia-aurea.tsv" fill="#D11141" radius="6">  
<param ve-map-layer geojson active title="Bihai" url="https://jstor-labs.github.io/plant-humanities/data/heliconia-bihai.tsv" radius="4.5" fill="#009900"> 

---

In this example, a map of the county of Kent in the UK uses the standard OSM basemap overlaid with a georeferenced topographic survey map from 1860.

<param ve-map center="51.254, 0.876" zoom="10">
<param ve-map-layer mapwarper active mapwarper-id="44832" title="Kent Topo Survey 1860">

---

This example uses the heatmap layer options.

<param ve-map center="-2, 118" zoom="4">
<param ve-map-layer heatmap 
       url="nepenthes_horticultural_heatmap.tsv" 
       radius="2" 
       scale-radius="true" 
       use-local-extrema="true" 
       max-opacity="0.6">