-`levels`: Array of objects that provides layer info
-`layerName`: Can be a string or function. Function takes argument as `properties` of parentLayer feature
-`layerOptions`: Same as layer options in `layers` option. If `url` is function, `url` takes argument as `properties` of parentLayer feature
-`legend`: configuration of legend to be added to layer. It requires [d3-legend](https://cdnjs.com/libraries/d3-legend). This creates a `<div class="map-legend">`.
-`position`: can be `topright`, `topleft`, `bottomleft` or `bottomright`(Defaults to `bottomright`)
-`format`: accepts d3 formats and applies to legend labels. (Defaults to `d`)
-`shape`: can be a d3 symbol or an svg path. Default `d3.symbolSquare`
-`size`: size of legend cell
-`cells`: number of cells in legend. Default `5`
-`width`: width of legend
-`height`: height of legend
-`scale`: accepts d3 scale format (mandatory). For examples, refer [d3-legend](https://d3-legend.susielu.com/#color-examples)
-`orient`: orientation of legend. Can be `vertical` (Default) or `horizontal`
-`shapeWidth`: width of legend cell. Default `20`
-`shapePadding`: padding of legend cell. Default `20`
-`labelOffset`: value to determine distance of label from each legend cell. Default `20`