Pls check the file contact-shortcodes.php line number 34 in {theme directory}/framework/shortcodes/ folder (and sendmail.php in the /scripts/ folder if you need to). You can modify the file to replace URL entry with City. Not very difficult; let me know if you run into issues.
Not sure how you would handle city validation other than telling someone that it needs at least a few characters in it. Pls check the validation for message like below in main.js file in {theme directory}/js folder –
message: {
required: true,
minlength: 15
}