Hi,

BY default in odoo itself, there is such functionality, if you go to partners form view, you can see a page named Partner Assignation, make sure that the module named base_geolocalize is installed in the database.

Once the module is installed you can see the latitude and longitude is coming based on the address of the partner on clicking the Geo Locate Button,

See the code of the corresponding button action:

@classmethod
def _geo_localize(cls, apikey, street='', zip='', city='', state='', country=''):
    search = geo_query_address(street=street, zip=zip, city=city, state=state, country=country)
    result = geo_find(search, apikey)
    if result is None:
        search = geo_query_address(city=city, state=state, country=country)
        result = geo_find(search, apikey)
    return result

@api.multi
def geo_localize(self):
    # We need country names in English below
    apikey = self.env['ir.config_parameter'].sudo().get_param('google.api_key_geocode')
    for partner in self.with_context(lang='en_US'):
        result = partner._geo_localize(apikey,
                                       partner.street,
                                       partner.zip,
                                       partner.city,
                                       partner.state_id.name,
                                       partner.country_id.name)
        if result:
            partner.write({
                'partner_latitude': result[0],
                'partner_longitude': result[1],
                'date_localization': fields.Date.context_today(partner)
            })
    return True

File in Github:  https://github.com/odoo/odoo/blob/13.0/addons/base_geolocalize/models/res_partner.py

Thanks