Joining tables to produce thematic maps

   Map object styles


   Using Expressions for Labeling

   Creating a Bivariate Thematic Map


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MapInfo provides two functions for labelling objects on the map using values extracted from the tabular data attached to each object:

the Label tool for labelling of individual objects. Click on the object to be labelled, at the point where the label is required;

an Automatic labelling function for labelling all the objects in a layer. Automatic labelling is switched on with the Label check box in the Layer Control dialogue.

Labels are part of the map window, not part of the table. The same objects can be labelled differently on different map windows.

Labels are attached directly to objects and are always editable, whether or not the layer to which dicy are attached is editable. Labels are always on top of other objects.

Configuring Labels
Prior to using the label tool or automatic labelling, use Map>Layer Control (Ctrl-L) to configure the labelling function. In the layer control dialogue, highlight the layer containing the objects to be labelled, and click the Label button to display the labelling options for the layer:

Labelling Field
Objects can be labelled with any of the fields defined for the table, or an expression (MapInfo Reference pages 194 - 195). This allows labelling with unique identifying information such as names (e.g. site or geographical names) or identifiers (e.g. site reference number, sampling IDs, object or event codes, street numbers).

String functions can be particularly useful as a means of truncating long fields or picking out short codes from the start or middle of a field, for example: Right$(SamplcID,4) to pick out the last four characters of an identifying number. Labels can also be created by coneatenating fields, for example: Mapsheet....... +Sitenum to concatenate the two fields separated by a dash (text between........... is reproduced verbatim). A line break can be inserted into the label with Chr$(10). To use an expression for labelling, select Expression ... at the bottom of the Source pulldown list. An existing expression can be edited by selecting Expression ... again.

Coded fields can be used to write a number or abbreviation for each object on the map as an alternative to the symbols provided by thematic mapping (chapter 8). This can be quite useful where there are a large number of values, so that letters A though Z or identifying codes may provide a better way of identifying objects than a plethora of symbols. The objects themselves can be replaced with the label by specifying N (no symbol) using the object style dialogue and centring the label (see below).

Custom labels
(labels created with the Label tool or labels dragged away from their original position or for which the style or content have been modified) are always visible. They are not affected by the visibility check box on the Layer Control dialogue or the visibility settings in the Label Options dialogue.

Automatic labels can be switched on and off by checking On or Off buttons in the Label Options dialogue, as well as by checking the Visible box in the Layer Control dialogue, or they can be displayed within a particular zoom range. A red check mark (-) in the labelling column of the Layer Control dialogue indicates that labels on that map layer are zoom layered, and that the map is zoomed outside the range of scales within which labels are displayed.

Where there are many labels the map can become a mess, so Maplnfo allows labels to eliminated selectively through Allow Duplicate Text, Allow Overlapping Text, and Maximum Labels. By uiichecidng duplicate text, you avoid multiple labelling of, for example, rivers which have been recorded in several short sections. Uncheeking overlapping text produces a clean map, but at the cost of losing labels for objects in proximity to one-another: this may be OK where one simply requires some representative labels rather than systematic labelling. Maximum labels sets an upper limit on the number of labels shown.

None of these options gives the user much control over what labels are shown and which are eliminated. A better option is often to allow both duplicate andoverlapping text, and then move the labels created to space them neatly, with lines or arrow lines back to the objects (see "Styles" below) where they have been moved substantially.

Previewing Labels
Because labels maintain a constant size relative to the map window, and are generally larger on the screen than on the printout of a map, it is very hard to position closely spaced labels on a map window. Zooming in shrinks the labels relative to the space available, so the result of zooining out again is unpredictable.

To obtain a semi WYSIWIG display of the final map, first adjust the map window to the final shape, orientation (portrait or landscape) and coverage of the map. Set the label size to the minimum acceptable for the final map, say 4 point (it is a good idea to use a compact serifed proportional font such as Times, as you can pack in a maximum amount of legible information in a small space). Don't worry about the appearance of the map, which is probably a mess of overlapping labels.

Now open a Layout window containing one frame for the map window, make sure the layout consists of one page (or more if you intend to print the map over multiple pages) in the same orientation as the map and resize the map frame (holding down Shift so that its shape doesn't change) to fill the layout. Position the layout window beside the map window and set it to view the layout at 100% or larger scale (Layout>Change Zoom).

Use Layout>Options and set Show frame contents to Always - this will ensure that the layout window is updated as each change is made in the map. If this proves too slow, change to Only when Layout Window is Active, which means you will have to activate the layout window after a few changes have been made to see the effect.

You can now adjust the position of the labels on the map and observe the final effect on the layout. The main difficulties are finding the label you want to move in the mess of labels on the map window (it may help to pull closely-spaced labels right out of the way and then move them back one by one) and finding the part of the map you are working on in the layout window.

The text style button allows setting of the font and styles (pages 118 - 119) to be used for labelling. Although Maplnfo only shows point sizes down to 8 point in the pulldown list, smaller point sizes can be typed into the dialogue and point sizes around 5 - 6 are often suitable for labelling large numbers of objects. Smaller point sizes can be used for output on a high resolution laser printer than are legible on the screen.

The point size of labels relative to the map window stays constant as the map is zoomed in and out, unlike text objects on map layers, which get larger as you zoom in (as did labels in MapInfo version 3).

When a label is dragged away from the object labelled, a plain line or an arrowed line can be drawn between the label and the object centroid (or the point labelled with the Label tool). Cheek the appropriate entry under Label lines. The style of the connecting line or arrow can also be changed using the line style button. Plain lines generally look better than arrows if there are lots of label lines.

Labels are positioned relative to the centroid' of the object they are labelling by clicking one of the Anchor Point boxes. The default 2 point Label Offset between the labels and the objects being labelled is often inadequate for point objects, resulting in a label which runs into the objects, and should be increased until the desired effect is obtained.

Checking the Rotate Label with Line box causes labels to follow the direction of the lines they are labelling so that, for example, grid lines in the Y direction will have text running vertically.

Labels, like other text objects, can be rotated individually, or several labels can be selected and rotated together, by dragging the rotation handle situated just below the right hand end of the text.

Missing Labels?
If you enable labels and find that only some of your objects have been labelled, check whether Allow Duplicate Text and Allow Overlapping Text have been enabled (page 140). If they are not, or if a limit has been specified under Maximum Labels, then labels will be eliminated from the map in a somewhat arbitrary manner. When a value is set for maximum labels, labels are displayed in the order in which the records occur in the table until the maximum number is reached, then no further labels are displayed.

If all your labels are missing, look to see whether a zoom range has been specified under Min. Zoom or Max. Zoom. Look for a red check mark in the labelling column in the Layer Control dialogue, which indicates that the map is outside the range of scales for which labelling has been enabled.

Text copied from:
Understanding MapInfo: A Structured Guide
Ian Johnson, 1996
Archaelogical Computing Library
University of Sydney, NSW

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