- (id) init {
    self = [super init];
    if (self != nil) {
        self.locationManager = [[[CLLocationManager alloc] init] autorelease];
		self.locationManager.distanceFilter = 25;
		
        self.locationManager.delegate = self; // send loc updates to myself
		
		_bTracking = NO;
		_bOneTime = NO;
    }
    return self;
}

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation
{
    NSLog(@"Location: %@", [newLocation description]);
			
	WebMercator *webMercator = [[WebMercator alloc]init];
	
	double webMercatorLongitude = [webMercator toWebMercatorX:newLocation.coordinate.longitude];
	double webMercatorLatitude = [webMercator toWebMercatorY:newLocation.coordinate.latitude];
	
		//create extent to be used as default
		AGSEnvelope *envelope = [AGSEnvelope envelopeWithXmin:webMercatorLongitude+0.0001
                                                     ymin:webMercatorLatitude-0.0001
                                                     xmax:webMercatorLongitude
                                                     ymax:webMercatorLatitude
													spatialReference:self.mapView.spatialReference];
    
		
		
		[self.mapView zoomToEnvelope:envelope animated:YES];	
	
		if ( _bTracking == NO)
			[self.locationManager stopUpdatingLocation];
		
		// Create the graphic layer for position if does not exist
		if ( self.trackGraphicsLayer == nil)
		{		
			// Add a point into the graphic layer with the correct attributes
			self.trackGraphicsLayer = [AGSGraphicsLayer graphicsLayer];
			
			//add graphics layer (data is loaded in mapViewDidLoad method)
			[self.mapView addMapLayer:self.trackGraphicsLayer withName:@"Track"];		
		}
		
		// Add a point where the gps finds you.		
		AGSPictureMarkerSymbol *myPicture = [AGSPictureMarkerSymbol pictureMarkerSymbolWithImageNamed:@"GpsDisplay.png"];
		
		AGSPoint* myMarkerPoint =
		[AGSPoint pointWithX:webMercatorLongitude
						  y:webMercatorLatitude
			spatialReference:self.mapView.spatialReference];
		
		//Create the Graphic, using the symbol and
		//geometry created earlier
		AGSGraphic* myGraphic =
		[AGSGraphic graphicWithGeometry:myMarkerPoint
								symbol:myPicture
							attributes:nil
						  infoTemplate:nil];
		
		//Add the graphic to the Graphics layer
		[self.trackGraphicsLayer addGraphic:myGraphic];
		
		//Tell the layer to redraw itself
		[self.trackGraphicsLayer dataChanged];	
		
				
		[webMercator release];
		
		return;
	}

Converting from WGS1984 to WebMercator:

#import "WebMercator.h"
#import <math.h>


@implementation WebMercator


- (double)toWebMercatorY:(double)latitude
{
	double rad = latitude * RADIANS_PER_DEGREES;
	double fsin = sin(rad);
	
	double y = 6378137 / 2.0 * log((1.0 + fsin) / (1.0 - fsin));
	
	return y;
}


- (double)toWebMercatorX:(double)longitude
{
	double x = longitude * 0.017453292519943 * 6378137;
	
	return x;
}

@end