GeoPointType.php

<?php 
namespace Acme\CommonBundle\Form\Type;

class GeoPointType extends AbstractType
{
    public function __construct($map)
    {
        $this->map = $map->get('ivory_google_map.map');
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->appendClientTransformer(new GeoToLatLongTransformer);
    }

    public function getParent()
    {
        return 'text';
    }

    public function getName()
    {
        return 'geo_point';
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults([
            'widget' => 'geo_point',
            'data_class' => 'Mashup\CommonBundle\Document\GeoPoint',
        ]);
    }

    public function buildView(FormViewInterface $view, FormInterface $form, array $options)
    {
        $this->map->setStylesheetOption('width', '100%');
        $view->setVar('map', $this->map);
    }
}

GeoToLatLongTransformer.php

<?php
namespace Acme\CommonBundle\Form\DataTransformer;

class GeoToLatLongTransformer implements DataTransformerInterface
{
    public function transform($geo)
    {
        return $geo->__toString();
    }

    public function reverseTransform($latlong)
    {
        return GeoPoint::createFromString($latlong);
    }
}

gistfile1.yml

acme.type.map:
        class: Acme\CommonBundle\Form\Type\GeoPointType
        arguments: [@service_container]
        tags:
            - { name: form.type, alias: geo_point }