That is so amazing! I also attempted creating such a concept but never got anyone of my friends to use it... I ended up heavily using (and abusing) the Google maps share your location feature and I was so excited to see they are adding features related to notifications when people get close - only noticed it a few months ago. Telegram had also released similar features but only when you share your location live witch you can only do for a limited amount of time. Nevertheless interesting to see these kind of features are slowly getting implemented even if easy too late and not close to how I would like and imagine they could be... I also have my live location broadcasted here: https://chagai.website/location.html when it's not broken