Magento – How to change the City Name to Drop Down on Checkout Page. Magento 2

app/code/Vendor/Checkout/etc/frontend/di.xml

Override layoutProcessor block for customize city field and change arguments of onepage block for render city options.

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Checkout\Block\Checkout\LayoutProcessor">
        <plugin name="checkout_layout"
                type="Vendor\Checkout\Plugin\LayoutProcessor" sortOrder="1"/>
    </type>
    <type name="Magento\Checkout\Block\Onepage">
        <arguments>
            <argument name="layoutProcessors" xsi:type="array">
                <item name="cityData" xsi:type="object">Vendor\Checkout\Block\Checkout\CityDataProcessor</item>
            </argument>
        </arguments>
    </type>
</config>

app/code/Vendor/Checkout/Plugin/LayoutProcessor.php

Initialize custom component and [import][initialoptions] to get city array in city.js

<?php

namespace Vendor\Checkout\Plugin;

class LayoutProcessor
{
    /**
     * @param LayoutProcessor $subject
     * @param array $result
     * @return array
     */
    public function afterProcess(
        \Magento\Checkout\Block\Checkout\LayoutProcessor $subject,
        array $result
    ) {
        $result['components']['checkout']['children']['steps']['children']['shipping-step']['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['city'] = $this->getConfig();

        unset($result['components']['checkout']['children']['steps']['children']['shipping-step']['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['region_id']);

        unset($result['components']['checkout']['children']['steps']['children']['shipping-step']['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['postcode']);

        $result['components']['checkout']['children']['steps']['children']['shipping-step']['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['telephone']['validation']['max_text_length'] = '11';
        return $result;
    }

    /**
     * @return $field
     */
    private function getConfig()
    {
        $field = [
            'component' => 'Vendor_Checkout/js/city',
            'config' => [
                'customScope' => 'shippingAddress',
                'template' => 'ui/form/field',
                'elementTmpl' => 'ui/form/element/select',
                'id' => 'city'
            ],
            'label' => 'City',
            'value' => '',
            'dataScope' => 'shippingAddress.city',
            'provider' => 'checkoutProvider',
            'sortOrder' => 80,
            'customEntry' => null,
            'visible' => true,
            'options' => [ ],
            'filterBy' => [
                'target' => '${ $.provider }:${ $.parentScope }.country_id',
                'field' => 'country_id'
            ],
            'validation' => [
                'required-entry' => true
            ],
            'id' => 'city',
            'imports' => [
                'initialOptions' => 'index = checkoutProvider:dictionaries.city',
                'setOptions' => 'index = checkoutProvider:dictionaries.city'
            ]
        ];


        return $field;
    }
}

app/code/Vendor/Checkout/Block/Checkout/CityDataProcessor.php

Add your city here, else better get cities from csv to avoid big array.

<?php
namespace Vendor\Checkout\Block\Checkout;

class CityDataProcessor implements \Magento\Checkout\Block\Checkout\LayoutProcessorInterface
{

    /**
     * Process js Layout of block
     *
     * @param array $jsLayout
     * @return array
     */
    public function process($jsLayout)
    {
        if (!isset($jsLayout['components']['checkoutProvider']['dictionaries']['city'])) {
            $jsLayout['components']['checkoutProvider']['dictionaries']['city'] = $this->getCityOptions();
        }

        return $jsLayout;
    }

    /**
     * Get country options list.
     *
     * @return array
     */
    private function getCityOptions()
    {
        //Add your city list here
        $options = [
            '1' => [
                'value'=>'city1',
                'name'=>'city1',
                'region_id'=>'1',//From database
            ],
            '2' => [
                'value'=>'city2',
                'name'=>'city2',
                'region_id'=>'2',//From databse
            ]
        ];

        if (count($options) > 0) {
            array_unshift(
                $options,
                ['title' => '', 'value' => '', 'label' => __('Please select a city.')]
            );
        }

        return $options;
    }
}

app/code/Vendor/Checkout/view/frontend/web/js/city.js

Render city options from initialoptions and filter with region_id

/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

/**
 * @api
 */
define([
    'underscore',
    'uiRegistry',
    'Magento_Ui/js/form/element/select',
    'Magento_Checkout/js/model/default-post-code-resolver',
    'jquery',
    'mage/utils/wrapper',
    'mage/template',
    'mage/validation',
    'underscore',
    'Magento_Ui/js/form/element/abstract',
    'jquery/ui'
], function (_, registry, Select, defaultPostCodeResolver, $) {
    'use strict';

    return Select.extend({
        defaults: {
            skipValidation: false,
            imports: {
                update: '${ $.parentName }.country_id:value'
            }
        },

        /**
         * @param {String} value
         */
        update: function (value) {
            var city = registry.get(this.parentName + '.' + 'city'),
                options = city.initialOptions,
                cityOptions = [];

            $.each(options, function (index, cityOptionValue) {
                //if(value == cityOptionValue.region_id){
                    var name = cityOptionValue.name;
                    var jsonObject = {
                        value: index,
                        title: name,
                        country_id: "",
                        label: name
                    };
                    cityOptions.push(jsonObject);
                //}
            });
            this.setOptions(cityOptions);
        }
    });
});

app/code/Vendor/Checkout/view/frontend/requirejs-config.js

/**
 * Copyright © 2018 EaDesign by Eco Active S.R.L. All rights reserved.
 * See LICENSE for license details.
 */

var config = {

    config: {
        mixins: {
            'Magento_Checkout/js/action/set-shipping-information': {
                'Vendor_Checkout/js/action/set-shipping-information-mixin': true
            }
        }
    }
};

app/code/Vendor/Checkout/view/frontend/web/js/action/set-shipping-information-mixin.js

Save city name instead of city value to database.

define([
    'jquery',
    'mage/utils/wrapper',
    'Magento_Checkout/js/model/quote',
], function ($, wrapper, quote, shippingFields) {
    'use strict';

    return function (setShippingInformationAction) {
        return wrapper.wrap(setShippingInformationAction, function (originalAction, container) {

            var shippingAddress = quote.shippingAddress(),
                shippingCity = $("#shipping-new-address-form [name = 'city'] option:selected"),
                shippingCityValue = shippingCity.text();

            shippingAddress.city = shippingCityValue;

            return originalAction(container);
        });
    };
});