Problem
A town needs public squares; they are the largest, most public, rooms that the town has. But when they are too large, they look and feel deserted.
Solution
Make a public square much smaller than you would at first imagine; usually no more than 45 to 60 feet across, never more than 70 feet across. This applies only to its width in the short direction. In the long direction it can certainly be longer.
Related Patterns
… this pattern forms the core which makes an Activity Nodes (30): it can also help to generate a node, by its mere existence, provided that it is correctly placed along the intersection of the paths which people use most often. And it can also help to generate a Promenade (31), a Work Community (41), an Identifiable Neighborhood (14), through the action of the people who gather there. But it is essential, in every case, that it is not too large.
An even better estimate for the size of the square: make a guess about the number of people who will typically be there (say, P), and make the area of the square no greater than 150 to 300P square feet - Pedestrian Density (123); ring the square around with pockets of activity where people congregate - Activity Pockets (124) ; build buildings round the square in such a way that they give it a definite shape, with views out into other larger places - Positive Outdoor Space (106), Hierarchy of Open Space (114), Building Fronts (122), Stair Seats (125); and to make the center of the square as useful as the edges, build Something Roughly in the Middle (126) …
Reference for full-text of Pattern: p. 310high-confidence