Learn how to execute a SQL query to access polygon 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 only a subset of your hosted data.
In this tutorial, you will perform server-side SQL queries to return a subset of features in the LA County Parcel feature layer. The feature layer contains over 2.4 million features. The resulting features are displayed as graphics on the map.
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 theFeature
module.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.
require([
"esri/config",
"esri/Map",
"esri/views/MapView",
"esri/layers/FeatureLayer",
], function(esriConfig, Map, MapView, FeatureLayer) {
Create a SQL selector
ArcGIS feature layers support a standard SQL query where clause. Use an HTML select element to provide a list of SQL queries for the LA County Parcel feature layer.
- Create a
parcel
array of SQL queries. Assign theType where
element to a SQL query from the array.Clause
const view = new MapView({
container: "viewDiv",
map: map,
center: [-118.80543,34.03000], //Longitude, latitude
zoom: 13
});
// SQL query array
const parcelLayerSQL = ["Choose a SQL where clause...", "UseType = 'Residential'", "UseType = 'Government'", "UseType = 'Irrigated Farm'", "TaxRateArea = 10853", "TaxRateArea = 10860", "TaxRateArea = 08637", "Roll_LandValue > 1000000", "Roll_LandValue < 1000000"];
let whereClause = parcelLayerSQL[0];
- Create a parent
select
element and addoption
elements for each SQL query. Add some some basic styles to the elements.
// SQL query array
const parcelLayerSQL = ["Choose a SQL where clause...", "UseType = 'Residential'", "UseType = 'Government'", "UseType = 'Irrigated Farm'", "TaxRateArea = 10853", "TaxRateArea = 10860", "TaxRateArea = 08637", "Roll_LandValue > 1000000", "Roll_LandValue < 1000000"];
let whereClause = parcelLayerSQL[0];
// Add SQL UI
const select = document.createElement("select");
select.setAttribute("class", "esri-widget esri-select");
select.setAttribute("style", "width: 200px; font-family: 'Avenir Next'; font-size: 1em");
parcelLayerSQL.forEach(function(query){
let option = document.createElement("option");
option.innerHTML = query;
option.value = query;
select.appendChild(option);
});
- Add the
select
element to thetop-right
corner of theview
.
// Add SQL UI
const select = document.createElement("select");
select.setAttribute("class", "esri-widget esri-select");
select.setAttribute("style", "width: 200px; font-family: 'Avenir Next'; font-size: 1em");
parcelLayerSQL.forEach(function(query){
let option = document.createElement("option");
option.innerHTML = query;
option.value = query;
select.appendChild(option);
});
view.ui.add(select, "top-right");
- Add an event listener to listen for
select
element changes.
view.ui.add(select, "top-right");
// Listen for changes
select.addEventListener('change', (event) => {
whereClause = event.target.value;
});
- Verify that the
select
element is created.
Create a feature layer to query
Use the Feature
class to access the LA County Parcel 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.
// Listen for changes
select.addEventListener('change', (event) => {
whereClause = event.target.value;
});
// Get query layer and set up query
const parcelLayer = new FeatureLayer({
url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
});
Execute a query
Use the query
method to perform a SQL query against the feature layer. The Query
will be autocast when the method is called.
- Create a
query
function withFeature Layer extent
parameter. Define aparcel
element and set theQuery where
property to thewhere
. Set theClause spatial
to only return features that intersect theProperty geometry
, which is restricted to the visibleextent
of the map. Theout
property will return only a subset of the attributes. Lastly, setFields return
toGeometry true
so that the features can be displayed.
// Get query layer and set up query
const parcelLayer = new FeatureLayer({
url: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0",
});
function queryFeatureLayer(extent) {
const parcelQuery = {
where: whereClause, // Set by select element
spatialRelationship: "intersects", // Relationship operation to apply
geometry: extent, // Restricted to visible extent of the map
outFields: ["APN","UseType","TaxRateCity","Roll_LandValue"], // Attributes to return
returnGeometry: true
};
}
- Call the
query
method on theFeatures parcel
usingLayer parcel
. 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(extent) {
const parcelQuery = {
where: whereClause, // Set by select element
spatialRelationship: "intersects", // Relationship operation to apply
geometry: extent, // Restricted to visible extent of the map
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.error);
});
}
- Update the event handler to call the
query
function when the selector changes.Feature Layer
// Listen for changes
select.addEventListener('change', (event) => {
whereClause = event.target.value;
queryFeatureLayer(view.extent);
});
- At the top-right, click Run. Choose a SQL query from the selector. At the bottom left, click Console to view the number of features returned from each query.
Display features
To display the features returned from the SQL query, add them to the view as polygon graphics. Define a pop-up also so the attributes can be displayed when features are clicked.
- Create a
display
function withResults results
as a parameter. Define asymbol
andpopup
variable to style and display a pop-up for polygon graphics. The attributes referenced match theTemplate out
specified in the query earlier.Fields
}).catch((error) => {
console.log(error.error);
});
}
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}"
};
// Assign styles and popup to features
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 returned to the
view
.
// Assign styles and popup to features
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 theFeature Layer display
function. Remove theResults console.log
.
parcelLayer.queryFeatures(parcelQuery)
.then((results) => {
console.log("Feature count: " + results.features.length)
displayResults(results);
}).catch((error) => {
console.log(error.error);
});
Run the app
In CodePen, run your code to display the map.
When the map displays, you should be able to choose a SQL query from the selector. The resulting features will be added to the map as polygon graphics. The SQL query is applied to the visible extent of the map.
What's next?
Learn how to use additional API features and ArcGIS services in these tutorials: