IFLA Section of Geography and Map Libraries

	IFLA Section of Geography and Map Libraries
If you have any suggestions, comments or items that you would like to see added to this collection, please direct your messages to: libmap1@uconnvm.uconn.edu

Title

Digital Map Librarianship: Working with Geodata: Digital Chart of the World

Digital Chart of the World
Let's step through the process of downloading the DCW data. First, the best general site about DCW data is The Digital Chart of the World (DCW) & Data Quality Project . This link keeps current. It is an excellent source site for information about the DCW. The DCW data was published in tiles of 5^o x 5^o, generally the same format as the paper product. Pennsylvania State University Library's Maps and Data Center has written an ARC/INFO routine to "clip" countries from tiles of data. This is a real enhancement to the user. Most users are more interested in the country (or county, town, political or administrative region) than they are in its geographic boundaries. The first screen allows the uer to select the continent. Both text and clickable map selections are possible.

Choosing the General Area
On the continent choice page (Europe in this case), be sure to notice the COORDINATE SYSTEM DESCRIPTION. In this case the projection is GEOGRAPHIC, the units are DD or decimal degrees and the spheroid is CLARKE 1866. The selection can only be made from the pull-down.

Choosing the Country's Coverages
Once the country is chosen, the next level of selection can take place. At this point a good understanding of what the various coverages include is necessary. While the checkboxes give good general descriptions, these can be deceptive. The U. S. Geological Survey provides a good listing of the DCW data layers. You can check the layers you want. Be selective. For some countries this selection can result in huge files. You might want to take one coverage at a time of all of a type such as all hydrographic data. You have the choice displaying the selections as a GIF... a map on the fly, or going ahead and extracting the data.

Previewing the Selection
The first step of the DCW Mapping Manager gives you an assessment of the selection. This is the last chance you will have to add or delete data from your selection. If you need to add layers, use the back button. What is really happening is that the check boxes are bulding a small ARC/INFO program job to extract the data from the latitude/longitude tiles of data. If you have trouble, it could be because there is competition for the machine. Remember, this is running in the map library at the Pennsylvania State University, not a business or corporation. When you submit the "job" a GIF image is generated.

Previewing the GIF Image
The second step of the DCW Mapping Manager presents a GIF image. The GIF image is an graphical representation of the geo-spatial dataset. You can previes the selections you have made with a graphical represention. Then you can download the data and bring it straight into a GIS software package such as ARC/INFO, ArcView, or convert and bring into MapInfo, IDRISI or any of the packages that allow for import ARC/INFO E00 exchange format files. This page reminds you what you have selected, and prompts you to select the CONTINUE button to download the data. The GIF image is not a geo-spatial dataset.

Selecting the Download Options
At this point, using the DCW Download Manager, you can select the download options for the selected data. You are also given the opportunity of downloading an ArcView project file.
This entire operation will take awhile. Keep your eye on the browser activity button to assure that the procedure is running, but otherwise, be patient.

Downloading the Data
This step compiles the data and compresses it according to the options you specified in the preceding steps. The file is now a "zip" or "tar.Z" file, some sort of compression. You will need a file compression software program in order to reconstitute it to its original format. But first, clicking on the "Download Coverage" button will

Determining the Action
But first, clicking on the "Download Coverage" button will send a message to your browser. In Netscape, under Options: General Preferences: Helpers, if the file type ZIP has as the action ASK USER, which is a default, you will get this report. Select the "Save File" button.

Saving the File to a Disk
At this point, Windows opens the "Save As..." action. You can save the file anywhere on your machine you like. Notice that the filename supplied by the DCW server is a unique number. Now is a good time to give it a name and a folder you are comfortable with. The file will download. Depending on the size of the file, the capacity of your modem and the traffic on the connection this could be a few minutes, or an hour or more. After the file has downloaded, you are finished with the DCW server. You might send the server operator a note. This is all still new enough that the anonymity of the transaction is odd for the library staff. He likes to get feedback. Remember, DCW is really a computer in the corner of a university map library.

Unzipping the Files
Once the files are local they can be decompressed using an unzip program. File names are not unique, so either rename the files according to your own naming conventions, or at the very least, keep coverages in seperate folders or sub-directories.
You are now ready to read the Readme file. Do it. Without this very important data documentation, the data is difficult at best.

Suggested Citation
McGlamery, Patrick, "Digital Map Librarianship: Working with geodata; Hands-on, Downloading from the WWW, Digital Chart of the World." Digital Map Librarianship: a working syllabus, 63rd IFLA Conference, Copenhagen, Denmark. (4, Sept. 1997. updated 9, Aug. 1999) <http://magic.lib.uconn.edu/ifla/wg_ho_dcw.htm>

Patrick McGlamery
Map Librarian
Map and Geographic Information Center
University of Connecticut Libraries
Storrs, CT 06268
libmap1@uconnvm.uconn.edu

Title	Digital Map Librarianship: Working with Geodata: Digital Chart of the World
Digital Chart of the World	Let's step through the process of downloading the DCW data. First, the best general site about DCW data is The Digital Chart of the World (DCW) & Data Quality Project . This link keeps current. It is an excellent source site for information about the DCW. The DCW data was published in tiles of 5^o x 5^o, generally the same format as the paper product. Pennsylvania State University Library's Maps and Data Center has written an ARC/INFO routine to "clip" countries from tiles of data. This is a real enhancement to the user. Most users are more interested in the country (or county, town, political or administrative region) than they are in its geographic boundaries. The first screen allows the uer to select the continent. Both text and clickable map selections are possible.
Choosing the General Area	On the continent choice page (Europe in this case), be sure to notice the COORDINATE SYSTEM DESCRIPTION. In this case the projection is GEOGRAPHIC, the units are DD or decimal degrees and the spheroid is CLARKE 1866. The selection can only be made from the pull-down.
Choosing the Country's Coverages	Once the country is chosen, the next level of selection can take place. At this point a good understanding of what the various coverages include is necessary. While the checkboxes give good general descriptions, these can be deceptive. The U. S. Geological Survey provides a good listing of the DCW data layers. You can check the layers you want. Be selective. For some countries this selection can result in huge files. You might want to take one coverage at a time of all of a type such as all hydrographic data. You have the choice displaying the selections as a GIF... a map on the fly, or going ahead and extracting the data.
Previewing the Selection	The first step of the DCW Mapping Manager gives you an assessment of the selection. This is the last chance you will have to add or delete data from your selection. If you need to add layers, use the back button. What is really happening is that the check boxes are bulding a small ARC/INFO program job to extract the data from the latitude/longitude tiles of data. If you have trouble, it could be because there is competition for the machine. Remember, this is running in the map library at the Pennsylvania State University, not a business or corporation. When you submit the "job" a GIF image is generated.
Previewing the GIF Image	The second step of the DCW Mapping Manager presents a GIF image. The GIF image is an graphical representation of the geo-spatial dataset. You can previes the selections you have made with a graphical represention. Then you can download the data and bring it straight into a GIS software package such as ARC/INFO, ArcView, or convert and bring into MapInfo, IDRISI or any of the packages that allow for import ARC/INFO E00 exchange format files. This page reminds you what you have selected, and prompts you to select the CONTINUE button to download the data. The GIF image is not a geo-spatial dataset.
Selecting the Download Options	At this point, using the DCW Download Manager, you can select the download options for the selected data. You are also given the opportunity of downloading an ArcView project file. This entire operation will take awhile. Keep your eye on the browser activity button to assure that the procedure is running, but otherwise, be patient.
Downloading the Data	This step compiles the data and compresses it according to the options you specified in the preceding steps. The file is now a "zip" or "tar.Z" file, some sort of compression. You will need a file compression software program in order to reconstitute it to its original format. But first, clicking on the "Download Coverage" button will
Determining the Action	But first, clicking on the "Download Coverage" button will send a message to your browser. In Netscape, under Options: General Preferences: Helpers, if the file type ZIP has as the action ASK USER, which is a default, you will get this report. Select the "Save File" button.
Saving the File to a Disk	At this point, Windows opens the "Save As..." action. You can save the file anywhere on your machine you like. Notice that the filename supplied by the DCW server is a unique number. Now is a good time to give it a name and a folder you are comfortable with. The file will download. Depending on the size of the file, the capacity of your modem and the traffic on the connection this could be a few minutes, or an hour or more. After the file has downloaded, you are finished with the DCW server. You might send the server operator a note. This is all still new enough that the anonymity of the transaction is odd for the library staff. He likes to get feedback. Remember, DCW is really a computer in the corner of a university map library.
Unzipping the Files	Once the files are local they can be decompressed using an unzip program. File names are not unique, so either rename the files according to your own naming conventions, or at the very least, keep coverages in seperate folders or sub-directories. You are now ready to read the Readme file. Do it. Without this very important data documentation, the data is difficult at best.
Suggested Citation	McGlamery, Patrick, "Digital Map Librarianship: Working with geodata; Hands-on, Downloading from the WWW, Digital Chart of the World." Digital Map Librarianship: a working syllabus, 63rd IFLA Conference, Copenhagen, Denmark. (4, Sept. 1997. updated 9, Aug. 1999) <http://magic.lib.uconn.edu/ifla/wg_ho_dcw.htm>