Data files used to produce post maps contain the X and Y coordinates used to locate points on the map. They can also provide additional information used to place labels on the map, define the symbols to use, the symbol size, the symbol color, and the angle at which each symbol is drawn. The first row of the data file may optionally contain the title for each column. These titles are used by the dialogs to associate a descriptive name with each column letter. Following the titles are the actual data, organized as one point (record) per row. Columns within the data file contain various properties for the point such as its X coordinate, Y coordinate, Z value, etc. The data must contain, at a minimum, the X and Y coordinates. Incomplete or blank records in the X and Y coordinate columns are not plotted on the map.
Data files used for post maps and classed post maps can contain slightly different information. Both types of files must contain X, Y coordinates used to locate the points on the map. In addition, data files for classed post maps should contain a column with data values used to determine the class for each point. If a third data column is not available for the Z coordinates for a classed post map, the first data column is used.
XY Coordinates in the Data File
The X and Y coordinates define the symbol locations and the extents of the post map. These coordinates can be in any columns in the data file, but Surfer assumes X is in column A and Y is in column B by default.
Z values in the data values, such as elevation or concentration, are associated with each X,Y location. This is typically the same column that was used when creating a grid file. Z values can be used to proportionally scale the posted symbols. You can define the minimum and maximum symbol size, and all points are scaled in proportion to these sizes. See Specifying Scaled Symbols for more information. Z values can also be used to assign colors to symbols. A colormap is defined based on the Z values and the symbols change color according to the colormap.
For classed post maps, the Z value is used to determine which class or bin will contain the data. Classes are based on specified data ranges, and each class is assigned a unique symbol. Classes can be saved and loaded for future use.
A common application for post maps and classed post maps is as overlays on contour maps. While the Z values used to scale the posted symbols in a post map, or to define the classes in a class post map, may be the same Z values used to generate the contour map, this is not required. For example, the posted symbols could be used to indicate rock type, while the contours show ore grade.
Data labels are text strings or numbers associated with each point on a post map. Labels may be the original data values for the data points, or may be other identifying text such as well names or sample numbers. Labels can use math text instructions to define custom character formatting.