Local Moran
Local indicators of spatial association or LISA is a class of local statistics that measure spatial association in sub-regions of the study region. They are often used to identify spatial outliers and local clusters.
The Local Moran statistic was suggested in Anselin (1995) as a way to identify local clusters and local spatial outliers. For more details, please read http://geodacenter.github.io/workbook/6a_local_auto/lab6a.html
function localMoran(
WeightResult w,
Array val,
Number permutations,
String permutation_method,
NUmber significance_cutoff,
Number seed)
Name | Type | Description |
w | WeightResult | the WeightResult object created from weights function |
val | Array | the values of a selected variable |
permutations | Number | the number of permutations for the LISA computation. Default: 999. |
permutation_method | String | the permutation method used for the LISA computation. Options are 'complete', 'lookup'. Default: 'lookup'. |
significance_cutoff | Number | the cutoff value for significance p-values to filter not-significant clusters. Default: 0.05. |
seed | Number | the seed for random number generator used in LISA statistics. Default: 123456789. |
Type | Description |
LisaResult | The LisaResult object contains the results of LISA computation: pvalues, clusters, lisa_values, neighbors, labels, colors |
Examples
Node.js
React
const jsgeoda = require('jsgeoda');
const fs = require('fs');
// load data
const data = fs.readFileSync('./data/natregimes.geojson').buffer;
// create jsgeoda instance
const geoda = await jsgeoda.New();
// load geojson in jsgeoda
const nat = geoda.readGeoJSON(data);
// create a queen contiguity weights
const w = geoda.getQueenWeights(nat);
// get HR60 values
const hr60 = geoda.getColumn(nat, "HR60");
// local moran statistics
const lm = geoda.localMoran(w, hr60);
import React, { Component } from "react";
import ReactDOM from "react-dom";
import DeckGL from "@deck.gl/react";
import { GeoJsonLayer } from "@deck.gl/layers";
import { StaticMap } from "react-map-gl";
import jsgeoda from "jsgeoda";
// Set your mapbox access token here
const MAPBOX_TOKEN =
"pk.eyJ1IjoibGl4dW45MTAiLCJhIjoiY2locXMxcWFqMDAwenQ0bTFhaTZmbnRwaiJ9.VRNeNnyb96Eo-CorkJmIqg";
// The geojson data
const DATA_URL = `https://webgeoda.github.io/data/natregimes.geojson`;
class App extends Component {
constructor() {
super();
this.state = {
mapId: "",
layer: null,
viewPort: {
longitude: -100.4,
latitude: 38.74,
zoom: 2.5,
maxZoom: 20
}
};
}
// load spatial data when mount this component
loadSpatialData(geoda) {
fetch(DATA_URL)
.then((res) => res.arrayBuffer())
.then((data) => {
// load geojson in jsgeoda, an unique id (string) will be returned for further usage
const nat = geoda.readGeoJSON(data);
const w = geoda.getQueenWeights(nat);
const hr60 = geoda.getColumn(nat, "HR60");
const lm = geoda.localMoran(w, hr60, 999, "lookup");
//const ue60 = geoda.get_col(nat, "UE60");
//const nmt = geoda.neighbor_match_test(nat, 5, [hr60, ue60]);
const lm_colors = lm.colors.map((c) =>
c
.toLowerCase()
.match(/[0-9a-f]{2}/g)
.map((x) => parseInt(x, 16))
);
// Viewport settings
const view_port = geoda.get_viewport(
nat,
window.innerHeight,
window.innerWidth
);
// Create GeoJsonLayer
const layer = new GeoJsonLayer({
id: "GeoJsonLayer",
data: DATA_URL,
filled: true,
getFillColor: (f) => this.getFillColor(f, lm.clusters, lm_colors),
stroked: true,
pickable: true
});
// Trigger to draw map
this.setState({
mapId: nat,
layer: layer,
viewPort: view_port
});
});
}
componentDidMount() {
// jsgeoda.New() function will create an instance from WASM
jsgeoda.New().then((geoda) => {
this.loadSpatialData(geoda);
});
}
// Determine which color for which geometry
getFillColor(f, clusters, colors) {
const i = f.properties.POLY_ID - 1;
const c = clusters[i];
return colors[c];
}
render() {
return (
<div>
<DeckGL
initialViewState={this.state.viewPort}
layers={[this.state.layer]}
controller={true}
getTooltip={({ object }) =>
object && `${object.properties.NAME}: ${object.properties.HR60}`
}
>
<StaticMap mapboxApiAccessToken={MAPBOX_TOKEN} />
</DeckGL>
</div>
);
}
}
ReactDOM.render(<App />, document.getElementById("root"));
Try it yourself in the playground (jsgeoda + deck.gl):