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Grid Maps

Grid-based maps include contour maps, image maps, shaded relief maps, vector maps, and wireframe maps, plus many other more application-specific maps.

Wireframe maps are three-dimensional representations of a grid file. Wireframe maps are block diagrams generated by drawing lines representing the grid X and Y lines (the grid columns and rows). At each intersection of a column and row (i.e. at each grid node), the height of the surface is proportional to the grid Z value at that point. The number of columns and rows in the grid file determines the number of X and Y lines drawn on the wireframe map.

Post maps indicate XY locations with symbols and labels. Posting data points on a map can be useful for determining the distribution and density of your data, as well as placing data or text information at specific locations on the map. You should be able to specify the symbol type, size, color, and angle for the data points.  In addition, good software such as Surfer will allow you to place an associated data value or text string next to the posted point. (As an aside, in Surfer you can also customize the size, angle, color, and typeface for the label.)

Post Maps vs Classes Post Maps

Two types of post maps are available: post maps and classed post maps. Post maps display a fixed or proportionally sized symbol at each data location. Classed post maps group the data into discrete classes (bins). The data points are displayed using the symbol and properties assigned to the class. Classed post maps should also include a legend.

Post maps can be used to show the spatial distribution of the original data when they are overlaid on a grid-based map (such as a contour map). This is often an excellent means of presenting a qualitative measure for the accuracy of the contour lines on the map (check to see if contouring software supports this feature ... Surfer does)

Post maps are created from data files containing X and Y coordinates. These coordinates are used to determine the locations for symbols on the post map. The data files can contain additional information used to size the symbols, determine the symbol angle, or post text associated with the point location.

Classed post maps group data points into classes according to their Z values. Each class is represented by a unique symbol. All points grouped in a single class are represented by the same symbol. Classed post maps require Z values in addition to the XY coordinates.

Z values are the data values, such as elevation or concentration, associated with each X,Y location. This is typically the same column that was used when creating a grid file. Z values are used to proportionally scale the posted symbols. You should be able to define the minimum and maximum symbol size, and specify that all points are scaled in proportion to these sizes. (In some packages you may need to purchase expensive add-on libraries to achieve this, but I have noted that this comes as standard in Surfer)

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.

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 in Post Maps

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.

The angle (in degrees) for the posted symbol can be specified in the data file for non-classed post maps. Positive angles rotate the symbols in a counterclockwise direction (again, this is a feature which comes as standard with the latest version of Surfer)