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1. Introduction
Appendix 2 - MM2 MINI- MANUAL 2: This document looks at how students can use the Digimap service to download raw digital files. All of the different map products available through Digimap can be downloaded and converted into a form compatible with ArcView and other GIS software. The document consists of two separate sections:
1. Using Digimap Download Digimap Download is perhaps the section of Digimap, which is of most value to GIS project students. Using this part of the web site you can identify and download your own digital files for use within ArcView. The map products available digitally include the following (layers relevant to the project are marked in bold): Strategi: 1:250,000 scale - general
topographic detail - 100% National Coverage. A tile refers to a single block of OS digital data and the geographical coverage of a tile will vary depending on the scale, i.e. a tile in Strategi covers an area of 20km x 20 km, whereas in Land-Line a tile is 500m x 500m. 1. Log on to Digimap. Click on the blue Advance Services button on the left. Then click on the button marked Digimap Download 2. There are a number of ways of working
out which tiles you need to download. If you know as we do in the sample
project then simple click on the box marked By Ordnance Survey Tile Name. 3. In the next screen, type in the tile name e.g. TQ20 and add a * wildcard character. This will find all tiles, which start with TQ20. A good way of narrowing in the search is to highlight the two products you need in the right hand box at the same time. You can select both Land-form Panorama DTM (not Panorama Contour) and Meridian at the same time by using the control button. Then click the View Tile Name box. 4. In the next screen highlight both found tiles in blue and continue. 5. The data is listed so just click on the Choose Data Format box. 6. The data you are downloading comes in tow formats. It is best to leave the default option - NTF - as this is the format that MapManager can use more easily. You MUST also click on the buttons at the bottom of the page asking for information on intended use. Click on the Learning button. Then simply click on the Extract data box and it will process for a while and deliver you a zipped up version of your files 7. You can then click on the zip file name (generally a long load of random text) and save in the correct sub-directory on your own computer. It's probably a good idea to rename it at the same time to something shorter like TQ20.zip. You can then close Digimap down. 8. Before you can use Map Manager properly you will also have to unzip the files within Windows to get at the .NTF file you need. Again you will have to shorten the names but we careful not to give them the same name as both the Panorama and Meridian file use similar named. It's probably a good idea to rename the Panorama file with a PAN at the start of the file name to distinguish it from the Meridian file. 2. Using Map Manager 6.2 to convert files into GIS format Almost all downloaded digital files are saved in the OS 's generic transfer format known as NTF (National Transfer Format). As it is generic, it is designed to be convertible into all different GIS. Each GIS tends to have it's own software conversion programme. The one developed by ESRI is called Map Manager and is installed on your computer. The final part of the exercise looks at a very simple file conversion session within Map Manager which allows you to produce a set of simple shape files which you can then load up in ArcView. Map Manager allows for a more sophisticated approach to NTF conversion which allows you to strip out only the layers you want and also allows you to merge and append the downloaded tiles together. This will be more easily explained on a one-to-one basis as the course develops and we will provide individual or small-group training in this as the module progresses. 2.1 Converting Panorama Files 1. Open up Map Manager and click on the Open Files icon. 2. Navigate to the directory where your NTF files are. They should appear on the right hand box. 3. Select the Panorama files (use shift click to select more than one) and click OK. 4. In the Selected files window, go to Windows > Output Format and then click on the Change Directory box. You will need to navigate to the directory where you want the converted files to go. You will also notice that the system defaults to the DTM Grid option as it knows it's dealing with a Panorama file. 5. Go to Window > Data Schema. Map Manager operates with 3 different windows and it is vital that you navigate between them using the drop down windows menu. If you close any of them then the whole system shuts down. 6. You've now got a screen in front of you with a number of options. For Panorama files you don't need to change anything. 7. Click on the RED ARROW icon and it will do the conversion for you. 8. Close down Map Manager. You will now have a new ASCII version of the file which you can import into ArcView 2.2 Converting Meridian2 Files The process of Converting Meridian2 files is broadly similar though a lot more complex at the end. Basically you select the files as in Steps 2 and 3 above. It differs from Step 4 onwards. 4. In the Selected files window, go to Windows > Output Format and then click on the Change Directory box. You will need to navigate to the directory where you want the converted files to go. Under Output Format you will need to click on the button marked Shape File Format. 5. Go to Window > Data Schema. Map Manager operates with 3 different windows and it is vital that you navigate between them using the drop down windows menu. If you close any of them then the whole system shuts down. 6. You've now got a screen in front of you with a number of options. You will notice that unlike the Panorama example there are lots of options available. For the exercise we have helped you by setting up the conversion process to convert to the layers you need using a template - known here as a Schema. 7. In the upper left hand box called Feature Code Attribute, click on the little button to the side and make sure that FEATURE CODE is highlighted. 8. Under the Load Schema Definition box click on the button to the right and you should find an option called Meridian. To check this is loaded properly navigate to the window below it marked Data Layers and click on the cross icon next to Coverage Layers. You should see 11 different layers in the list. This means that the conversion will group all the data and create the separate layers you need. 9. Click on the RED ARROW and it will convert each of the selected layers in turn. You'll see some progress bars running along the bottom of the screen as it processes. Do not close anything once it's finished. 10. To amalgamate the tiles you have created (this will save a lot of time and energy in the GIS) simply go the drop down menu Utilities > Append shape files. You will then be asked to navigate to the directory where you want the files to go. You should then see a list in the right hand box of the 11 layers. Select them all and then click OK. 11. The files will now be available as a set of amalgamated shape file in a sub-directory called Appended in your working directory. They can then be used for the Criteria modelling in ArcView |
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prev | back to class materials | back to top Last updated: December 4, 2003
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