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Map Room Home page | |
written by Nigel
James
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MAPINFO How to... | |
No. 9: Using raster (scanned) maps and photos | |
(References to tables, folders etc., are not applicable outside the Map Room, so if you are located elsewhere, you should substitute your own) | |
This explains how to use raster (scanned) maps and photos in MapInfo. MapInfo How to No 10 (Manual Geocoding) should be used as well for information on using thematic data with raster images. MapInfo How to No.1 should be used for step-by-step instructions on creating and saving maps and layouts. See the user guide and other How to guides for information on using tools etc. MapInfo How to No.1 should be used for step-by-step instructions on creating and saving maps and layouts. |
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These procedures assume your map is not already geo-referenced. If you have a geo-referenced image, such as a Landsat GeoTIFF and you have MapInfo version 7.0 or later, you can open the image without registering it first, but you will still have to select the correct projection. | |
The datasets used in MapInfo use vector data. This can be rescaled without loss of image quality and the various features are on separate layers so details can be displayed selectively. A raster or scanned image is simply a picture made up from individual pixels (picture x elements). Rasters images cannot be rescaled without losing image quality, so can only be used at around their original size and the detail cannot be separated into layers. Raster maps can be used as a background or base map, with symbols etc. added using the Cosmetic Layer. If you wish to add data using coordinates, then the raster map has to registered, which involves defining coordinates for at least three separate points on the map and requires the original map projection to be known. Digital pictures can be used simply as images to enhance your layouts. |
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IMPORTANT: Maps and photos are protected by copyright, so if the photos are not your own, or the maps are 70 years old or less, you cannot use them without permission of the copyright owner. OS maps are protected by Crown Copyright. US Government mapping is public domain and may be used without further permission. You are responsible for ensuring that you are not infringing copyright. The library does not have scanning facilities for readers' use, so you will have to obtain your images yourself from other sources. | |
1. To open your scanned map in MapInfo, open the file as you would a table, but select Raster Image in the Files of type box. | |
2. You will be asked if you wish to simply display the map or register it (define coordinates). To use the map (or photo) just as an image, click Display. To register the image, click Register, then go to step 5. | |
3. The map will appear in a mapper window. Use a combination of window size and zoom level to display the map approximately at its correct scale. To display the map at its true scale, you must know the exact dimensions of the map (in miles or km). You can the set the window width and zoom level precisely. | |
4. You can add extra details on the cosmetic layer, using the drawing tools. | |
5. If you wish to register your map, you must add a minimum of three control points (and know the projection of the original map). Alternatively, you can use non-earth coordinates to create a basic coordinate system which will enable you to map thematic data. (See MapInfo Howto no.9 for more information). For an OS raster image, use the intersections of the gridlines, for other types of mapping you will need to identify precise known coordinate points. | |
6. To add a control point, use the zoom buttons (+ -) and scroll bars to move the map around and locate a suitable point. Select the correct projection and units by clicking the buttons and selecting the required settings. Click on the map to select a point. | |
7. Enter the X and Y coordinates and label them if you wish. Coordinates can be modified later if necessary. | |
8. Repeat for at least two more points. MapInfo interpolates the coordinates, so the more you select (and the more widely spaced) the more accurate the registration will be. | |
9. When you have entered the coordinates, click OK and you can use the map as with any other layer. Raster maps which have been registered can be used with data tables to produce thematic maps, using coordinates to locate points which can display pie charts, for example (See: MapInfo How To No. 10). | |
10. Maps and photos can be added to the Layout window in the usual way. You will need to adjust the size of the frame so that the image displays at an acceptable level of quality. | |
11. To adjust the image (brightness and contrast) , make the raster image window active, then open the Table menu, click Raster, then Adjust Image Styles. Make any changes and click OK. If you are adding your own data, it may be preferable to change the map to a greyscale image, so that added line, symbol and text will show more clearly. To do this, click Grayscale in the Conversions box on the Adjust Image Styles dialog. | |
12. To make a colour transparent (so that other layers show through the raster image, click the Transparent box and then click a suitable colour (such as the white background in an OS map). Click OK to confirm. | |
13. When resizing the map in the layout window, the map will enlarge or reduce accordingly. This is different to a vector map, which stays the same scale but increases or decreases the area displayed. Because of this it is important to set the area required in the mapper window, then set the scale in the layout window. To scale the map, measure a known distance (such as between grid lines) against the rulers on the layout window. When resizing the layout map, always hold down the SHIFT key whilst dragging the corner resize handles. This will stop the map becoming stretched or distorted. | |
This is a brief and specific guide to this topic, for more general information, see: MapInfo l - an easy guide for new users | |
Nigel
James
Bodleian Library 2001 |