If you have added attributes to the objects (pointnodes and lines) that you created (see Edit Attribute Fields and Edit Attributes ), you may use those attributes to select groups of objects for display with graphic characteristics that you specify, instead of the default red dots and black lines. Your specifications are kept in a list, with each entry in the list specifying the graphic characteristics to be used for a selected group of objects.

An object may belong to more than one group, and thus will be affected by more than one specification. So the final graphic characteristics of each object result from the cumulative effect of all specifications that apply to it. If something in a later specification contradicts something in an earlier specification, the one that appears later in the list will override the first.

The Graphic Characteristics item in the Edit menu brings up the Edit Graphic Characteristics window, and allows you to add and edit entries in this list. That item has a cascading menu which allows you to choose Pointnodes or Lines. We'll discuss pointnodes first.

The Edit Graphic Characteristics window has a list of entries. When you start a new file, you have not made any entries, so the list will contain only a line of three dots that represents the end of the list.


To add an entry click on the line of dots.


The line is highlighted and the Insert button becomes available.


Click the Insert button.


The new entry appears highlighted and ready for editing. Since you have not yet defined a selection rule for this entry, it is simply listed as <no selection rule>.


Click the Edit button to define the new entry.

The Edit window opens. For pointnodes, this window is very large because there are many graphic characteristics available for pointnodes. For lines, the window will be smaller, and is discussed below.

Most of the items in the window are initially unavailable (grayed-out). Two text items at the top and five buttons on the left are available (as well as the usual OK and Cancel).

We will discuss these items one at a time.

(NOTE: Many of the following examples show the results of changes made in this window. Keep in mind that changes won't actually be made to your map until you click OK.)

Point to the Selection Rule box and type a selection rule. A selection rule usually consists of three items: an operand, a comparison operator, and another operand. The first operand is the name of an attribute field. The last operand is either another attribute field name, a value, or the keyword "$var".

In the example shown here, the selection rule given will cause any pointnode that has the word "village" in the field named "type" to be selected for this specification.

The keyword "$var" will use the current value of the user variable (see Edit Variables).

Comparison Operators

Operator	Meaning
==	equal
<	less than
>	greater than
<=	less than or equal
>=	greater than or equal
!=	not equal

If either operand is a numeric field, a date field, or "$var", the comparison will be numeric (e.g., the number "11" is greater than the number "2"). Otherwise the comparison will be a string comparison using the ASCII sort order (e.g., the string "11" is less than the string "2").

You may also use the keyword "$all" for the first operand. If so, anything typed after "$all " will be ignored (and can be handily used as a comment). Using "$all" will cause all pointnodes to be selected for this specification.

The selection rule is mandatory. If you click OK without entering a valid selection rule, an error message will pop-up describing the problem.

The description is optional. If you include a description it will appear in the overlay legend (see View Legend.) Otherwise, this specification will not affect the overlay legend. (It will still affect the overlay map.)

The graphic for a pointnode consists of three parts:

• The label
• The symbol
• The ring

• Those that affect the label
• Those that affect the symbol
• Those that affect the ring
• Those that affect both the symbol and the ring
• Those that affect all parts.

The three toggle buttons in the label group become available. With these buttons you choose which of the label characteristics you wish to change.



To change the label text, click the Text button.

The text box becomes available.

Point to the text box and type in your entry. This can be any text that you want to use for all pointnodes that match the selection rule, or it can be the name of an attribute field. In the latter case, the actual text used for each pointnode will be the text found in that field of its record.

In the example, "name" is the name of an attribute field.


The pointnode will be displayed with a label consisting of the text in its "name" field.


To change the label style, click the Style button.

The style menu buttons become available. The first four buttons affect the label font, and the last two affect its color.

Initially all of the font properties are set to "*" -- the wildcard character, the foreground color is set to black, and the background color is set to clear. This means that the first font found will be used, and drawn in black with a transparent background.

To get more specific about the font, use the menu buttons to set properties. In this example the font's family has been set to "Times" and its point size has been set to 18, while its weight and slant properties are still set to wildcards. So the first font found from the "Times" family with a point size of 18 will be used.


Here is the result of the above change: an 18-point "Times" font. In this case it looks like the weight is "bold", and the slant is "Italic". On another system it might find a different weight and/or slant. To be absolutely sure of consistency between systems it is best to specifically set all properties.

To make the label easier to read on a busy map, you may select a background color other than "clear". This will cause a rectangle of the chosen color to appear behind the text.

In this example, the background color has been set to "yellow".


Here is the result of the above change.

The font Weight menu contains an item called "Two-tone". This is not a standard font property, but is specific to XViewSDTS. When a "Two-tone" weight is used, the background is not rectangular, but appears to follow (roughly) the outline of the characters. It works better with the larger point sizes than it does with the smaller ones. "Two-tone" is only available for fonts from the "Courier" family, and you must specify the slant and point size (that is, you can't use "*").

In this example, a 24-point, italic "Two-tone" font has been chosen, with red foreground and green background.


Here is the result of the above change.


To change the label position, click the Position button.

The position menu button becomes active, and shows the default position. Below are the results of setting it to each of the four possible positions.


Right

Left

Below

Center

Using the "Center" position for a label with the default red dot symbol isn't very pleasing. Normally the "Center" position is used when there is either no symbol, or a symbol designed to have a label placed on it, as in the following example.

In this example, the label text "495" has been positioned on the center of a highway shield symbol (interstate3.xpm). Symbols will be discussed next.


OK, we are done playing with the label. For now we'll keep the label text that we set, but go back to the default label style and label position (by clicking the Style and Position toggle buttons so that they are no longer set).

The single toggle button in the symbol group becomes available.


Click the Name/Style button.

The Name: box and the Style menu button become available.

Point to the name box and type the name of the symbol you wish to use. This is usually the name of an XBM file or an XPM file in one of the symbol directories listed in your run control file (see Editing Run Control Files).

(Hint: You may also enter an absolute pathname or a pathname that is relative to your symbol directory, but it is not recommended. Using pathnames may be useful when you are developing a map, as it will allow you to use image files that have not yet been placed in one of the symbol directories. But because pathnames will be dependent on the structure of your filesystem, you should not use pathnames in files that you share with others, or will use yourself on other systems.)

You may also enter the name of an attribute field. In that case the filename (or pathname) is taken from that field in each pointnode's record. Thus, the pointnode can specify its own symbol.

If you don't want any symbol (not even the default red dot) enter the word "none" for the name.

In this example, the XBM file dot2.xbm has been chosen.


The chosen symbol is displayed -- a dot with two circles around it. The label moves over a bit to make room for it.

Symbols usually are transparent, allowing the background of the map to show through.

Here the map has a red area. The red shows through the symbol.

By changing the symbol style from "Centered" to "Opaque Centered", the symbol will now obscure the map.


In this case the pixels that were normally transparent are now white.

"Opaque Centered" is something that you probably will use only rarely. The other symbol styles, "Tiled" and "Opaque Tiled", are useful only when working with rings, and will be discussed below in the section on rings.

Setting the symbol name to "none" and the symbol style to "Centered" will eliminate the symbol altogether.


Here is the pointnode displayed with a label, but no symbol.


If a symbol file cannot be located, a question mark is shown.

The single toggle button in the symb/ring group becomes available.


Click the Color button.

The Color menu button becomes available.

Use the Color: menu to choose your desired color. This will change the ring color and the color of symbols from XBM (X bitmap) files only -- XPM (X pixmap) files define their own colors.


The symbol color is changed.

The three toggle buttons in the ring group become available.


To change the radius, click the Radius button.

The Radius box and Units menu button become available.

Point at the Radius box and enter a value. This can either be a number, or the name of an attribute field. If the latter is the case, the radius is taken from that field in each pointnode's record.


A ring is drawn around the symbol.

The Unit menu button allows you to change the unit of measure. The unit can be either pixels or a linear unit of measure. When units are pixels, the ring will always be drawn the same size on the screen when you zoom in and out. If you choose a linear unit, the size of the ring on the screen will vary with the map scale, increasing when you zoom in and decreasing when you zoom out.


Ring with 1 kilometer radius at a scale 50 meters per pixel.


Ring with 1 kilometer radius after zooming to a scale of 25 meters per pixel.


Choosing "<other>" from the unit menu brings up the Unit window. Point to the Unit Length box and enter the length in meters of the unit you wish to use.


Then click OK.

Your chosen unit appears on the Unit menu button.


The ring is redrawn with the new radius.


To change the line width, click the Line width button.

The Width box becomes available.

Click the + or - buttons to set a value. Alternatively, you may point at the Width box, backspace to clear the current value, and enter a new integer value in the range of 0 to 15. (A line width of 0 is not invisible, but is actually drawn with a width of 1 pixel. What makes 0 different from 1 here is the fact that setting the value to 0 may take advantage of the line drawing features of your graphics hardware and so may speed up the drawing a bit.)


The ring is redrawn with the new line width.


To change the dash style, click the Dash style button.

The first On box becomes available.

Click the + or - buttons to set a value. Alternatively, you may point at the On box, backspace to clear the current value, and enter a new integer value in the range of 0 to 99. Any non-zero vale causes the first Off box to become available.

Set a value for the number of pixels that will be off -- that is, the space between the dashes. Again, the range is 0 to 99. Any non-zero vale causes the second On box to become available, but you don't need to use it for simple dashed lines where all dashes are the same length, and all spaces between dashes are the same length.


The ring is redrawn with the new dash style. Because each dash is rounded off, they hang over a bit into the space between the dashes. So if the "Off" value is the same as the line width, the ring will appear more like a string of linked sausages than a dashed line.

If you like, you may increase the "Off" value to put some space between the dashes.


The ring is redrawn with the new dash style.

To fill the ring with a pattern, go up to the Symbol group and set the symbol name to your desired pattern, and the symbol style to "Tiled".

(Hint: Because drawing large rings using the "Tiled" symbol style can take a lot of processing time, you may not want to use that style with more than a few rings, unless the rings will be small and you don't plan on zooming in too far.)

You may also use the "Opaque tiled" symbol style, but that, of course, will obscure the area of the map under the ring.

The ring is filled with the pattern.

The single toggle button in the overall group becomes available.


Click the Visibility button.

The Visibility menu button becomes available.

Use the Visibility menu to choose the desired visibility.

In this example visibility is set to "Hidden".


The pointnode's label, symbol, and ring are all hidden.

That's all for the Edit window for pointnodes. Next comes the Edit window for lines.

The graphic characteristics Edit window for lines is not as large as the Edit window for pointnodes. There are only four graphic characteristics that may be set for lines. Better yet, the window contains nothing that hasn't already been discussed above.

The Selection Rule and Description boxes are used exactly the same way for pointnodes and lines.

And the four characteristics are set just like they were above for pointnodes. (See Color, Line Width, Dash Style, and Visibility.)

That's all for the Edit window for lines.

(Hint: You may insert at another place in the list by clicking on that place before clicking Insert.)  


The line of dots moves down and is replaced by a new entry which is highlighted and ready for editing. Click Edit to set the selection rule and graphic characteristics as already explained.


When you finish editing, the new selection rule replaces "<no selection rule>" in the list. Perhaps you would prefer it higher in the list? If so, click Move Up .


The entry is moved up. Move Down, not surprisingly, does the opposite. But maybe you've decided that you didn't want that entry after all. Click Delete.


The field is deleted. Maybe you've changed your mind again? If so, click Undelete.


The Undelete window appears. It has a list of entries that you have deleted since you've been editing this Graphics Characteristics file. Click the entry you want to undelete.


The field is highlighted. Click OK.


The Undelete window disappears, and the entry is restored to the list in the Edit Graphic Characteristics window, at the highlighted position.

You may continue adding entries until you have specified all of the graphic characteristics for your objects. When you are finished, you may click Close, or if you think you'll need this window again soon, you may simply move it out of your way and leave it open. It is possible to continue working with this window open.

(Hint: If you try to open it again and find that the entry in the Edit menu is grayed-out, it is probably already open, just hidden by other windows. Look in your window manager's window menu.)

Perhaps the best way to learn about the various characteristics is to experiment. You are encouraged to create a test map with a single pointnode. Then create a graphic characteristics specification with the keyword "$all" as the selection rule. Repeatedly edit that specification to try out different characteristics.

Copyright © 2005 by Dapper Mapper