A rate surface for diabetic patients attending the Los Angeles County-USC Medical Center. Figure 1 displays the geographic extent of the Los Angeles County study area displayed as an Inverse Distance Weighted (IDW) smoothed grid of all those patients who made ED visits whose primary diagnosis was diabetes related. This is expressed as a rate (per 1000 ED visits), therefore, the highest rate is almost 370/1000. This means, if 1000 patients attended the ED with diabetes, the primary diagnosis was directly related to a health problem resulting from that disease (in effect one of the ICD codes investigated in this paper) - this being their reason to seek medical attention. The outer red box identifies the larger study area which was included to assess the stability effect of spatial scale.