Salesforce and Google Maps API to calculate distance borrowed from: http://bulkified.com/How+to+use+the+Google+Maps+API+in+Salesforce.com

googlemaps.apxc

public class googleMaps {

	public String duration {get;set;}
	public Integer travelTime {get;set;}
	public Decimal distance {get;set;}

	public googleMaps(
			String address1,
			String address2) {
				
		String jsonResults = getJsonResults(address1, address2);
		jsonResults = formatJsonResults(jsonResults);
		updateJsonSections(jsonResults);
	}

	public String getJsonResults(
			String address1,
			String address2) {
		
		HttpRequest req = new HttpRequest();
		Http http = new Http();
		
		req.setMethod('GET');
		
		String url = 'https://maps.googleapis.com/maps/api/distancematrix/json'
			+ '?origins=' + address1
			+ '&destinations=' + address2
			+ '&mode=driving'
			+ '&sensor=false'
			+ '&language=en'
			+ '&units=imperial';
			
		req.setEndPoint(url);
		
		HTTPResponse resp = http.send(req);
		
		String jsonResults = resp.getBody().replace('\n', '');

		return jsonResults;
	}
	
	public String formatJsonResults(String value) {
		
		value = value.replace('{', ', ');
		value = value.replace('}', ', ');
		value = value.replace('[', ', ');
		value = value.replace(']', ', ');
		value = value.replace('"', '');
		
		return value;	
	}
	
	public void updateJsonSections(
		String jsonResults) {
		
		List<String> jsonSections = jsonResults.split(', ');
		
		for (Integer i = 0; i < jsonSections.size(); i++) {
			jsonSections[i] = jsonSections[i].trim();
			
			if (jsonSections[i].contains('duration:')) {
				duration = parseDuration(jsonSections[i + 2]);
				travelTime = parseTravelTime(duration);
			}
			
			if (jsonSections[i].contains('distance:')) {
				distance = parseDistance(jsonSections[i + 2]);
			}
		}
	}

	public Decimal parseDistance(String value) {
		value = value.replace('text: ', '');
		value = value.replace(' mi', '');
		value = value.replace(' ft', '');
		value = value.replace(',', '');
		value = value.trim();
		
		return Decimal.valueOf(value);
	}
	
	public String parseDuration(String value) {
		value = value.replace('text: ', '');
		
		return value;
	}
	
	public Integer parseTravelTime(String value) {
	
		Integer tmpMinutes = 0;
	
		List<String> durationNodes = value.split(' ');
		String prevDurationNode = '';
		
		for (String durationNode : durationNodes) {
			if (durationNode == 'day' || durationNode == 'days') {
				tmpMinutes += Integer.valueOf(prevDurationNode) * 1440;
			}
			if (durationNode == 'hour' || durationNode == 'hours') {
				tmpMinutes += Integer.valueOf(prevDurationNode) * 60;
			}
			if (durationNode == 'min' || durationNode == 'mins') {
				tmpMinutes += Integer.valueOf(prevDurationNode);
			}
			
			prevDurationNode = durationNode;
		}
	
		return tmpMinutes;	
	}

}

googlemaps_test.apxc

public class test_ctrl_GoogleMaps_Accounts {

	/* Constructor */
	public test_ctrl_GoogleMaps_Accounts() {
		updateAccounts();
	}

	/* Accounts */
	public List<Account> accounts = new List<Account>();
	
	public List<Account> getAccounts() {
		return accounts;
	}
	
	public void updateAccounts() {
		accounts =
			[SELECT Id, Name, ShippingStreet, ShippingCity,
				ShippingState, ShippingPostalCode, ShippingCountry
			 FROM Account
			 WHERE ShippingStreet <> ''
			 LIMIT 100];
	}
	
	/* Account Variables */
	public String account1Id {get;set;}
	public Account account1 {get;set;}
	public String account1Address {get;set;}
	
	public String account2Id {get;set;}
	public Account account2 {get;set;}
	public String account2Address {get;set;}
	
	public void updateAccountVariables() {
		for (Account a : accounts) {
			if (a.Id == account1Id) {
				account1 = a;
			}
			if (a.Id == account2Id) {
				account2 = a;
			}
		}
	}
	
	public void updateAccountAddresses() {
		account1Address = EncodingUtil.urlEncode(
			+ account1.ShippingStreet + ' '
			+ account1.ShippingCity + ', '
			+ account1.ShippingState + ' '
			+ account1.ShippingPostalCode + ' '
			+ account1.ShippingCountry,
			'UTF-8');
			
		account2Address = EncodingUtil.urlEncode( 
			+ account2.ShippingStreet + ' '
			+ account2.ShippingCity + ', '
			+ account2.ShippingState + ' '
			+ account2.ShippingPostalCode + ' '
			+ account2.ShippingCountry,
			'UTF-8');
	}
	
	/* Account Options */
	public List<selectOption> getAccountOptions() {
		
		List<selectOption> options = new List<selectOption>();
		
		for (Account a : accounts) {
			options.add(new selectOption(a.Id, a.Name));
		}
		
		return options;
	}
	
	/* Button Action */
	public void btnCalculateDistance_Click() {
		
		updateAccountVariables();
		updateAccountAddresses();
		
		googleMaps gm = new googleMaps(
			account1Address,
			account2Address);

		distance = gm.distance;
		duration = gm.duration;
		travelTime = gm.travelTime;
	}
	
	/* Results */
	public Decimal distance {get;set;}
	public String duration {get;set;}
	public Integer travelTime {get;set;}

}

mapstest.vfp

<apex:page controller="test_ctrl_GoogleMaps_Accounts">
    
    <apex:form >
    
        <apex:pageBlock title="Google Maps">
        
            <apex:pageBlockSection columns="1">
            
                <apex:pageBlockSectionItem >
                
                    <apex:outputText value="Account #1" />
                    <apex:selectList value="{!account1Id}" size="1">
                        <apex:selectOptions value="{!accountOptions}" />
                    </apex:selectList>
                
                </apex:pageBlockSectionItem>
            
                <apex:pageBlockSectionItem >
                
                    <apex:outputText value="Account #2" />
                    <apex:selectList value="{!account2Id}" size="1">
                        <apex:selectOptions value="{!accountOptions}" />
                    </apex:selectList>
                
                </apex:pageBlockSectionItem>
            
            </apex:pageBlockSection>
            
            <apex:pageBlockButtons location="bottom">
            	
            	<apex:commandButton id="btnCalculateDistance"
            		value="Calculate Distance" action="{!btnCalculateDistance_Click}"
            		rerender="pbResults" />
            	
            </apex:pageBlockButtons>
        
        </apex:pageBlock>
        
        <apex:pageBlock id="pbResults" title="Results">
        
        	<apex:pageBlockSection columns="1">
        		
        		<apex:pageBlockSectionItem >
        		
        			<apex:outputText value="Distance (miles)" />
        			<apex:outputText value="{!distance}" />
        		
        		</apex:pageBlockSectionItem>
        		
        		<apex:pageBlockSectionItem >
        		
        			<apex:outputText value="Duration" />
        			<apex:outputText value="{!duration}" />
        		
        		</apex:pageBlockSectionItem>
        		
        		<apex:pageBlockSectionItem >
        		
        			<apex:outputText value="Travel Time (minutes)" />
        			<apex:outputText value="{!travelTime}" />
        		
        		</apex:pageBlockSectionItem>
        		
        	</apex:pageBlockSection>
        
        </apex:pageBlock>
    
    </apex:form>
    
</apex:page>