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#### A.4.2.3 Defining Subsets Graphically

The plot windows can be used to define new Row Subsets by indicating a screen region containing the points of interest. Depending on the type of plot, one or more of the following options will be available as toolbar/menu items:

- Subset From Visible
- Algebraic Subset From Visible
- Draw Blob Subset
- Draw Algebraic Subset

In all these cases, when you have graphically specified a region, a dialogue box will pop up to ask you the name of the corresponding subset(s). As described in Section 3.1.1, it's a good idea to use a name which is just composed of letters, numbers and underscores. You can optionally select a subset name which has been used before from the list, which will overwrite the former contents of that subset. When you enter a name and hit the OK button, the new subset will be created and added to the list shown in the Subset Window, and the points in it will be shown straight away on the plot using a new symbol. As usual, you can toggle whether the points in this subset are displayed using the Subsets tab in the table layer control.

The different options for making these graphical selections are described in the following subsections.

- A.4.2.3.1 Subset from Visible
- A.4.2.3.2 Algebraic Subset From Visible
- A.4.2.3.3 Draw Blob Subset
- A.4.2.3.4 Draw Algebraic Subset

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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@jiscmail.ac.uk