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#### A.5.4.1 Table Layer Control

The Table layer control () is available for all the plot types. Use the Layers menu item or corresponding toolbar button to add an instance to the control stack.

This is the control which is used for most of the data plotting in the layer plot windows. Each instance of this control in the stack does plotting for a particular set of positions from a single table. The set of positions is defined in the Positions tab as a column name or expression for each plot coordinate (e.g. for X and Y in a plane plot). However, the control can generate multiple layers from these positions; the Subsets tab controls which subsets are plotted and how each one is identified, and the Form tab provides many options for what graphics will be plotted based on the positions.

The three tabs, Position, Subsets and Form, are described in more detail below.

Position tab of Table layer control

In the Position tab you enter the base positions for each plotted point. This generally means selecting a table and providing a value (table column or expression) for each positional coordinate. When you first open a plot window, TOPCAT gives you a table layer control by default, and attempts to fill in the positional coordinates with some reasonable values from the table (for instance the first few numeric columns).

Subsets tab of Table layer control

The Subsets tab lists the defined Row Subsets for the table you have selected in the Position tab. The subset All is always present; others may or may not be depending on whether any have been defined. Note that actions you take in the plot (for instance selecting a new subset by region) can result in new entries being added to this list.

The list on the left names the subsets with an activation checkbox and a grab handle; the panel on the right gives the detail for the currently selected subset. Select a subset to see/change its detail by clicking on it.

For each subset you can select:

- Whether it is plotted (using the activation checkbox)
- The plotting sequence (by dragging it up and down using its grab handle)
- The default plotting colour
- The label with which it is annotated in the legend (if visible)
- Whether it appears in the legend at all

Although you can select plotting colours in the Form tab as well, it's generally better to do it here since this changes the colour of all the forms plotted for a given subset, rather than one form at a time.

Form tab of Table layer control

The Form tab lets you define how each data set is plotted. The list on the left gives a list of forms currently being plotted, and the panel on the right shows the detailed configuration for the currently selected form.

When first added, the list contains a single entry, Mark, which plots a marker of a given fixed shape and size. The colour is by default determined by the setting in the Subsets tab. For a simple scatter plot, this is all that you need. However, there are a number of other forms that you can plot as well or instead of the simple markers - vectors, error bars, ellipses, contours, text markers etc. You add a new form to the stack by clicking on one of the buttons in the toolbar in the tab. You can remove a form with the Remove () button in the same toolbar. You can also activate/deactivate them with the checkbox and move them up and down with the drag handle as usual. The list of forms that are avaiable depends on the plot type; the full list is in Appendix A.5.5.

The detail panel of each form depends on the form itself. It is divided into the following panels, though not all forms have all the panels.

Shading
  The shading mode controls how points are shaded based on their chosen colour. The various options are described in Appendix A.5.6. Depending on the mode there may be more settings to fill in here.
Coordinates
  If additional coordinates are required for this form, for instance the size of error bars, you need to enter the column or expression here. Each coordinate effectively adds another dimension to the plot. Some forms, like Mark, do not require any additional coordinates.
Global Style
  Controls the style details for the chosen form, for instance marker shape and size. Options here affect all subsets, though by default the colour is taken from the Subsets tab.
Subset Styles
  If you want to have different subsets represented with different styles, for instance different shapes for different subsets, you can select a subset here and alter style details for that subset only, overriding the Global settings above.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@bristol.ac.uk