The Z-Variate is the variate being analyzed and mapped, e.g. elevation for a topographic map, pH for a map of soil acidity, chlorophyll content for a map of lake productivity, population density for a map of rural population growth. A Worksheet can contain many variates but only one can be analyzed at a time, thus only one column can contain the Z-Variate data. A Z-Variate Column must be defined prior to spatial analysis. To specify a column, click on the top row of the GS+ Worksheet. Variates can be named at the top of the column.