Mapinfo Tips

1. How to select a object below an other object which are in the same layer

Select the select button tool, hold the control key and select the object which is below an other object, Now the object which is below will be selected.

2. How does the Auto trace function works

In Mapinfo Ver. 4.1 you have a new feature called auto trace. Which is very useful. Using this you can save time in re-digitising. So how does this work.

1. Make sure that the snap is ON, if not, set the snap by pressing "S" key on the keyboard

1. Select the polyline or region command to start tracing, Know snap on a vertex Pt 1 of an existing polygon, this is the start point.
2. Move to the point Pt 2, and place the cursor so that the cross hair appears, showing that it has snapped. Do not click here... wait.
3. Now if you want to trace a line from Pt 1 to Pt 2 along "a" (ie. Shortest route) then hold the shift key and click at the point Pt 2, or if you want to trace along "b" (ie longest route) then hold the control key and click at the point Pt 2.
4. Now you have a polyline traced over this.

This is how the auto trace works, but you have a restriction. For the auto trace to work, both the points, in this example Pt 1 and Pt 2 should be on the same polygon. So make sure that if you are tracing, both the points are on the same polygon.

3.How to select objects by their graphic properties

I have a table with few polylines, regions, points and lines. I want all the polylines to be selected and attributed it as drainage. How do I select only the polylines from this.

1.Open the table and make the layer editable.

2.From the Query menu select SQL Select command.

3.Now I wanted all the polylines from the table ‘test" to be select.

4.Key in the conditions as shown below

5. Now you have all the polylines from the table "test" selected into the table "Polylines".
6. In the same way if you want to select other features,
7. To select line - Str$(obj) = "line"

• region - Str$(obj) = "region"
• rectangle - Str$(obj) = "rectangle"

Now that I have selected the polylines. I can update the column by the Update Column command. And add the attribute drainage to all the polylines in the table.

4. Recovering Data After a Crash

When changes are made to a MapInfo table, the updated information is stored in temporary files, with the extensions .TIN, .TDA and .TMA. When the changes to a table are saved, the changed records are moved from the temporary files to your table, and the temporary files are deleted. If your system crashes with edits pending, these temporary files still be on your hard disk and you may be able to recover lost data by doing the following:

If for example you are editing a file called MyTable, you should have files called MyTable.tin, MyTable.tda and MyTable.tma out on the hard drive. What you can try is renaming the temporary files to MyTable1.ind, MyTable1.dat and MyTable1.map. You may then be able to open the MyTable1 in MapInfo and recover you changes.

So no worries when mapinfo close all of a sudden, and you have not saved the file. Just rename the temporary files.

Compiled by M.Suresh Babu

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