Abstract: This paper argues that grid-based spatial reasoning can significantly improve human-computer interaction. While grids constrain the user’s ability to position objects on a screen on one hand, they greatly increase the transparency of functional relationships among these objects on the other hand. A system called Agentsheets employes the notion of agents organized in a grid. The spatial relationships between agents are used to capture design properties independent of domain and programming language. Two types of spatial relations are distinguished called strict-spatial relations and pseudo-spatial relations. This paper gives a short introduction to Agentsheets, explains how Agentsheets address problems of construction kits, sketches sample applications, and evaluates the contribution of grid-based spatial reasoning to human-computer interaction.