Form Ds are filed with the United States Securities and Exchange Commission to show new business funding. Every startup is required to file how much money they have raised and this data is available from the commission. This site adds the daily filings to Google Maps so that users can see which companies around them are starting up and/or expanding.
From the map you can see the hubs of startup activity in the US on a daily basis. The map updates in real-time throughout the day as new filings arrive at the SEC. A quick look at the map at 7 am (EST) will show the map largely empty but by the evening it will be full of map markers displaying new business financings.
The map could also be a good source for people to see new businesses in their area that might be hiring. Every business that files a Form D has new funds to spend!