1

My question is, how can I get Leaflet to color each of circleMarkers I am generating/points with a different color, based off the type property of the point?

I've done a bit of research, but all I've seen is coloring points based on manually created dictionary, while my "known list of types" can be expanded at any time, and additional colors have to be added to accommodate new types of points. Also I am quite weak in Javascript and its actual syntax.

I have the list of all unique types before the iteration over data.

I am working in C# MVC if that helps.

My view (presentation layer of the program - generates a HTML page based off its contents) iterates over Model data (basically data which I need to show on the map) which contains latitude, longitude and type properties (more than that, but irrelevant for this), and adds the points to map, drawing them.

Code that generates my points:

{
foreach (var item in Model)
{
    <text>var point = L.circleMarker(["@item.Latitude",     "@item.Longitude"]).addTo(mymap)
        .bindPopup("@item.Type.TypeDesc" + ", " + "@item.Latitude" + ", " +     "@item.Longitude" + ", " + "@item.RPT_DT").openPopup(); </text>
}
}

I need each point to be of a color depending on TypeDesc property. List of TypeDesc properties can be easily accessed via a Viewbag.TypeDesc list.

0

OP here, I solved the problem.

So basically the solution boiled down to either: 1. Hard coding the values in a color picker function. 2. Picking a color from a program-generated gradient (basically I set a start and a finish and iterate). 3. Picking from a palette.

  1. Would've been the most accurate solution, since then lets say Type[big] will always have color red. But it's ugly as hard coding usually is.
  2. Wouldn't really satisfy my needs, I need colors and not gradients. While it's possible to get granular colors from gradients, it becomes a program of its own.
  3. I took random colors from https://gist.github.com/mucar/3898821 and used is as palette. I iterated through my categories, e.g. I have categories 0-50. And if the category matches the value, I take the corresponding color in palette.

function(input){ define color palette; compare input with each of possible categories; index of matching category in list of categories = index of color from the palette; return color; }

Consequence of solution 3 : if I add new categories, all categories have a different color. However, all categories have their same respective colors, always, until a new category is added.

0

Elaborating on the third option in OP's answer:

Code

I'm assuming that you have an array of points with coordinates and categories. This differs slightly from the OP's question. Using the ES6 standard of JavaScript and palette.js from Google, you can automatically colour your points like this:

//Get an array of unique categories
//Reference: [1]
var uniqueCategories = [...new Set(points.map(function(point) {
    return point.category
}))]

//Create palette ('mpn65' has up to 65 different colours)
var palette = palette('mpn65',uniqueCategories.length);

//Construct empty JavaScript Map (keys mapped to values)
//Reference: [2]
var paletteMap = new Map()

//Map all categories to a RGB colour string
for(let i = 0; i < palette.length; i++) {
    paletteMap.set(uniqueCategories[i],palette[i])
}

//Add circleMarkers to Leaflet map
for (let point of points) {
  L.circleMarker(point.coordinates,
                 {color: '#' + paletteMap.get(point.category)} //retrieve mapped colour
                ).addTo(map)
}

Links

[1] https://stackoverflow.com/questions/1960473/get-all-unique-values-in-a-javascript-array-remove-duplicates#14438954
[2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

Working example

There is a working example hosted on Codepen: https://codepen.io/anon/pen/zmNLdZ?editors=0010#0

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