Astrometry using wide field coded aperture cameras is the most effective way to obtain prompt locations of gamma ray bursts for observations by narrow field instruments. However, the rate of burst detections using this method has been disappointing. In an attempt to understand this problem, I have been investigating the scaling relationships between instrument characteristics and instrument performance. The ideas are very simple, but the results are sometimes counter‐intuitive.I will discuss the effects of field of view and detector area on detected burst rate. I will also discuss the relationship between instrument architecture and instrument volume, a major limitation and cost driver. I will show how attention to these relationships could lead to an inexpensive mission capable of locating bursts at a very high rate. © 2004 American Institute of Physics