Learn how to execute a spatial query to access features from a feature layer.
A feature layer can contain a large number of features stored in ArcGIS. To access a subset of the features, you can execute either a SQL or spatial query, or both at the same time. You can return feature attributes, geometry, or both attributes and geometry for each record. SQL and spatial queries are useful when you want to access just a subset of your hosted data.
In this tutorial, you will use the Sketch
widget to draw a feature and then perform a spatial query against a feature layer. The query layer is the LA County Parcels feature layer containing ±2.4 million features. The spatial query uses the sketched feature to return all of the parcels that intersect.
Prerequisites
You need an ArcGIS Developer or ArcGIS Online account to access the dashboard and create an API key.
Steps
Create a new pen
- To get started, either complete the Display a map tutorial or .
Set the API key
To access ArcGIS services, you need an API key.
- Go to your dashboard to get an API key.
- In CodePen, set the
api
to your key, so it can be used to access basemap layer and location services.Key
esriConfig.apiKey = "YOUR_API_KEY";
const map = new Map({
basemap: "arcgis/topographic" // basemap styles service
});
Add modules
- In the
require
statement, add theSketch
,Graphics
, andLayer Feature
modules.Layer
The ArcGIS Maps SDK for JavaScript is available as AMD modules and ES modules, but this tutorial is based on AMD. The AMD require
function uses references to determine which modules will be loaded – for example, you can specify "esri/Map"
for loading the Map module. After the modules are loaded, they are passed as parameters (e.g. Map
) to the callback function where they can be used in your application. It is important to keep the module references and callback parameters in the same order. For more information on the different types of modules, visit the Introduction to Tooling guide topic.
"esri/config",
"esri/Map",
"esri/views/MapView",
"esri/widgets/Sketch",
"esri/layers/GraphicsLayer",
"esri/layers/FeatureLayer"
], function(esriConfig, Map, MapView, Sketch, GraphicsLayer, FeatureLayer) {
Create a sketch widget
Use the Sketch
and Graphics
classes to create a graphic. The graphic will be added to the map in a graphics layer. The event handler will listen for a change from the sketch widget and update the query accordingly.
- Create a
graphics
and add it to theLayer Sketch map
.
const view = new MapView({
container: "viewDiv",
map: map,
center: [-118.80543,34.03000], //Longitude, latitude
zoom: 13
});
// Add sketch widget
const graphicsLayerSketch = new GraphicsLayer();
map.add(graphicsLayerSketch);
- Create a
sketch
widget and set thelayer
property tographics
. Add the widget to the top-right of theLayer Sketch view
.
// Add sketch widget
const graphicsLayerSketch = new GraphicsLayer();
map.add(graphicsLayerSketch);
const sketch = new Sketch({
layer: graphicsLayerSketch,
view: view,
creationMode: "update" // Auto-select
});
view.ui.add(sketch, "top-right");
- Create an event listener that will update each time a graphic is drawn. This will run a new query.
view.ui.add(sketch, "top-right");
// Add sketch events to listen for and execute query
sketch.on("update", (event) => {
});
- You should see the sketch widget at the top right of the view. Click on one of the options in the widget to draw on the map.
Create a feature layer to query
Use the Feature
class to perform a query against the LA County Parcels feature layer. Since you are performing a server-side query, the feature layer does not need to be added to the map.
- Create a
parcel
and set theLayer url
property to access the feature layer in the feature service.
Feature layers are referenced by an index number at the end of the url. To determine the index number, visit the LA County Parcels feature service. In this case the index is 0
.
// Add sketch events to listen for and execute query
sketch.on("update", (event) => {
});
// Reference query layer
const parcelLayer = new FeatureLayer({
url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
});
Execute the query
Define a parcel
and use the Feature
query
method to execute a query.
- Create a
query
function withFeaturelayer geometry
as a parameter and defineparcel
. Set theQuery spatial
toRelationship intersects
and use thegeometry
from the sketch widget. Limit the attributes returned by setting theout
property to a list of fields. Lastly, setFields return
toGeometry true
so the feature geometriescan be displayed.
// Reference query layer
const parcelLayer = new FeatureLayer({
url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
});
function queryFeaturelayer(geometry) {
const parcelQuery = {
spatialRelationship: "intersects", // Relationship operation to apply
geometry: geometry, // The sketch feature geometry
outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
returnGeometry: true
};
}
- Call the
query
method on theFeatures parcel
using the parameters defined in theLayer parcel
element. To view the number of features returned, write the result length to the console. This will be updated in the next step.Query
function queryFeaturelayer(geometry) {
const parcelQuery = {
spatialRelationship: "intersects", // Relationship operation to apply
geometry: geometry, // The sketch feature geometry
outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
returnGeometry: true
};
parcelLayer.queryFeatures(parcelQuery)
.then((results) => {
console.log("Feature count: " + results.features.length)
}).catch((error) => {
console.log(error);
});
}
- Update the event handler to call the
query
function every time a graphic is sketched on the map. It will also listen for any reshape or move changes made to the graphic.Feature Layer
// Add sketch events to listen for and execute query
sketch.on("update", (event) => {
// Create
if (event.state === "start") {
queryFeaturelayer(event.graphics[0].geometry);
}
if (event.state === "complete"){
graphicsLayerSketch.remove(event.graphics[0]); // Clear the graphic when a user clicks off of it or sketches new one
}
// Change
if (event.toolEventInfo && (event.toolEventInfo.type === "scale-stop" || event.toolEventInfo.type === "reshape-stop" || event.toolEventInfo.type === "move-stop")) {
queryFeaturelayer(event.graphics[0].geometry);
}
});
- Use the widget to draw a graphic. At the bottom left, click Console to view the number of features returned from the query.
Display features
To display the parcel features returned from the query, add them to the view as polygon graphics. Before the graphics are added, define a symbol and a pop-up so that the attributes can be displayed when a feature is clicked.
- Create a
display
function. Define aResults symbol
andpopup
variable to style and display a pop-up for polygon graphics. The attributes referenced match theTemplate out
specified in the query earlier.Fields
const parcelQuery = {
spatialRelationship: "intersects", // Relationship operation to apply
geometry: geometry, // The sketch feature geometry
outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
returnGeometry: true
};
}
// Show features (graphics)
function displayResults(results) {
// Create a blue polygon
const symbol = {
type: "simple-fill",
color: [ 20, 130, 200, 0.5 ],
outline: {
color: "white",
width: .5
},
};
const popupTemplate = {
title: "Parcel {APN}",
content: "Type: {UseType} <br> Land value: {Roll_LandValue} <br> Tax Rate City: {TaxRateCity}"
};
}
- Assign the
symbol
andpopup
elements to each feature returned from the query.Template
const popupTemplate = {
title: "Parcel {APN}",
content: "Type: {UseType} <br> Land value: {Roll_LandValue} <br> Tax Rate City: {TaxRateCity}"
};
// Set symbol and popup
results.features.map((feature) => {
feature.symbol = symbol;
feature.popupTemplate = popupTemplate;
return feature;
});
- Clear the existing graphics and pop-up, and then add the new features to the
view
as graphics.
// Set symbol and popup
results.features.map((feature) => {
feature.symbol = symbol;
feature.popupTemplate = popupTemplate;
return feature;
});
// Clear display
view.closePopup();
view.graphics.removeAll();
// Add features to graphics layer
view.graphics.addMany(results.features);
- Update the
query
function to call theFeaturelayer display
function. Remove theResults console.log
.
parcelLayer.queryFeatures(parcelQuery)
.then((results) => {
console.log("Feature count: " + results.features.length)
displayResults(results);
Run the app
In CodePen, run your code to display the map.
When you use the widget to sketch a feature on the map, the spatial query runs against the feature layer and returns all parcels that intersect the sketched feature.
What's next?
Learn how to use additional API features and ArcGIS services in these tutorials: