Checking Regions - MapInfo_Pro - 2023

You can check region maps for possibly badly formed objects with the Check Regions command, which is available by selecting the object you want to check and on the SPATIAL tab, in the Edit group, click Check Regions from the list.

Check Regions detects errors in your data that may produce problems or incorrect results when various operations are performed. There are a couple of rules associated with the Check Regions dialog box. You must select the regions you want to check before you use the Check Regions command. The objects must reside in one layer, and they must all be closed objects. MapInfo Pro places the Check Regions results in the current editable layer in the active Map window. There is no data aggregation or disaggregation performed on this data and no data is associated with the objects created. The options for the Check Region dialog box are explained in detail in this section. To see examples of the gap and overlap regions, see the illustrations at the end of the Cleaning Objects section.

The Self-Intersection Detection option helps you to check your regions for areas that cross over themselves, which could cause errors later on. When you use this option, the Check Regions command creates a point at the location where the data may self intersect. To change the symbol used to indicate self intersections, click the Style button in the Self-Intersection Detection group to display the Symbol Style dialog box. You can make the desired changes here.

The Overlap Detection option checks the data for places where regions overlap each other. When you use this option, the Check Regions command creates regions that represent any areas of overlap. To change the fill of the overlap regions, click the Style button in the Overlap Detection group to display the Region Style dialog box. You can make the desired changes here.

The Gap Detection option checks the data for places where region boundaries do not line up, causing a space or gap between regions. Some gaps in boundary data may be naturally occurring, such as a lake. Generally, gaps that are errors are caused by misaligned boundaries, and are generally small. A maximum gap area must be entered for gap detection. Gaps larger than this area are ignored and not flagged. This should help differentiate natural gaps, such as lakes, from misalignment errors. To change the fill of the gap regions, click the Style button in Gap Detection group to display the Region Style dialog box.

To use the Check Regions command:

1. Make sure your Map window is active and that you have an editable layer.
2. Select the region object(s) that you want to check.
3. On the SPATIAL tab, in the Edit group, click Check Regions to open the Check Region Objects dialog box.
4. To check for self-intersections, select the Detect Self-Intersection check box. The Symbol Style button enables. The check box is set by default.
5. To check for region overlaps, select the Detect Overlays check box. The Style button for Overlap Detection enables. The check box is cleared by default.
6. To check for gaps, select the Detect Gaps check box. The Region Style button, the Maximum Gap Area, and the Area Units are activated. The check box is cleared by default.
7. Click the Symbol Style button to change the symbol style used to indicate the location style of the self intersections.

   If you specified Overlap Detection, click the Region Style button to change the fill pattern for the regions that represent the areas of overlap.

8. Click OK. Your map redraws, and the self intersections, overlapping regions and gaps, if specified, are displayed.

   If you specified Gap Detection, check the Region Style button in the Gap Detection group to change the fill pattern and color used to represent gaps.

The settings are retained per session and per layer. When you close MapInfo Pro and reopen the program, the Overlap Detection check box is reset to the default. If you select another layer, Overlap Detection is also reset to the default (not selected). This per-session and per-layer scheme is also used in other operations such as Buffer Objects and Convex Hull.

Check Regions does not correct your data; it only shows the location of the incorrect data.

Checking Regions/Tables for Incorrect Data

You can check regions/tables for various aspects of incorrect data, or possible incorrect data, which may cause problems and/or incorrect results in various operations. Only region objects will be checked. The region objects will be checked for self-intersections and will check for overlapping objects if desired.

Some of the problem areas checked include:

• Line segments within a region, which cross each other.
• Nodes within a single polygon of a region where the polygon touches itself. The node will have more than 2 line segments emanating from it. This case can be broken down into two other instances. Given a polygon that has 2 looped sections, if the path traced by the nodes of the polygon follow a cursive figure 8, then this is called a figure 8. If the same 2 looped polygon can have its path traced as a cursive capital letter B, then this is termed a Bow Tie. Figure 8's are considered to be worse than Bow Ties. For example, the Area of a Figure 8 will always be incorrect, while the area of a Bow Tie will be correct and accurate. Figure 8's and Bow Ties are both detected.
• Gaps that are closed areas between regions that do not contain objects. While some gaps may be legitimate (e.g., the Great Lakes between the United States and Canada in the WORLD.TAB map), small gaps often reflect poor boundary matches between regions. Overlaps may similarly represent poor boundary matches.

To check for incorrect data:

1. Select the Map window you want to check, making it the active window.
2. Select an object in the Map window.
3. Make the map layer with the selected object editable.
4. On the SPATIAL tab, in the Edit group, click Check Regions to open the Check Region Objects dialog box.
5. You can change the symbol used to denote self-intersections by clicking the Self-intersection Detections button. The Symbol Style dialog box displays, which allows you to select your own symbol. Once a symbol is selected you can continue.
6. Check the Overlap Detection box and click OK.

If there were no data problems, a dialog box displays with the message,

Check region did not find any data problems.

If there were data problems, a point object is created and placed into the output table. If you select to check for overlapping objects, then the overlapped regions will be placed in the output table.

Detecting and Correcting Self-Intersections, Gaps, and Overlaps

When you add a street to a map, it may cross existing streets. Usually, this indicates that the streets intersect (except in the case of an overpass, where there is no intersection). You may want to perform Overlay Nodes onto Target so that MapInfo Pro adds a node to each street at the point of intersection. Once the streets have a common node, MapInfo Pro's Find command is able to locate the intersection of the two streets. To find an intersection, enter two street names in the Find dialog box, separated by a pair of ampersand characters (e.g. "Broadway && River St").

To detect and correct self-intersections, gaps, and overlaps:

1. Select the objects you want to work with.
   Note: All of the objects selected must either be closed objects (for example, regions, rectangles, rounded rectangles or ellipses) or linear objects (for example, lines, polylines, or arcs). The selection cannot contain a mixture of closed and linear objects.
2. Make the table containing the objects editable.
3. On the SPATIAL tab, in the Edit group, click Clean Objects in the list to open the Clean Objects dialog box.
4. Check Remove Overlaps and/or Gaps. If you choose Gaps, you need to specify Maximum Gap Area and Area Units.
5. Click OK.

See Also:

Clean Objects Dialog Box