GIS Data Unzipping Procedures
December 30, 1999
The GIS Management Office (GISMO) is responsible for distributing data from the Southern Nevada GIS Central Repository. Data is provided to Interlocal Agencies and their subcontractors, to GIS Data Subscribers and to the public. The purpose of this document is to discuss the zip files provided by the GIS Management Office. The topics discussed in this document are technical in nature and therefore may not be for everyone. As always, please E-mail your comments to the Clark County GIS Management Office.
The Southern Nevada GIS Central Repository employs a directory structure that begins with /gisdata and contains subdirectories for each major collection of data. For example, Street Centerline data is stored in /gisdata/crscl and Election data is stored in /gisdata/crel. For better or worse, users must become familiar with these pathnames to derive the greatest benefit from the Southern Nevada GIS Central Repository.
Here is a list of the primary subdirectories used:
Directory Description Directory Description CRAIR Aviation Department CRFLOOD Regional Flood Control District CRCLV City of Las Vegas CRLVVWD Las Vegas Valley Water District CRCOMP Clark County Comprehensive Planning CRMETRO Metropolitian Police Department CREL Election Department CRNLV City of North Las Vegas CRHEND City of Henderson CRPARKS Clark County Parks Department CRFIRE Clark County Fire Department CRPCL Assessor's Office Tabular and Miscellaneous Data CRGEN General Points of Interest CRPW Clark County Public Works CRGEO General Geography CRSAND Clark County Sanitation District CRIMAGE Digital Imagery CRSCL Street Centerline LIBBK Library of primarily Clark County Easments. There is one zip file for the whole library of coverages (ie. libbk-src.zip). There are no associated shapefile zip. LIBLU Library of Landuse including Zoning, Resolutions-of-Intent, Existing Landuse and Planned Landuse. All the available Landuse data from the separate jurisdictions (ie. Boulder City, City of Las Vegas, Clark County, Henderson and North Las Vegas) is stored here. Each section is zipped into a separate file (ie. liblu14034-wksp.zip). There are no associated shapefile zips. LIBPCL Library of Assessor's Office Parcels. Each section is zipped into a separate file (ie. libpcl14034-wksp.zip). There are no associated shapefile zips. For most /gisdata subdirectories, GISMO has created one zip file for coverages and one zip file for shapefile data. For example, there are several coverages related to the Street Centerline database in the /gisdata/crscl directory structure including cities (sclcity), census tracts (scltract), zip codes (sclzip), annotation (sclan), etc. However, these individual coverages will be aggregated into one zip file (ie. crscl-src.zip) for all of the coverages and one zip file (ie. crscl-shp.zip) for all of the associated shapefile data.
The exceptions for the one zip file for coverages and one zip file for shapefile per subdirectory are the library structures libbk, liblu and libpcl. First, none of these libraries will have shapefiles. Second, zip files are created for each PLSS section of data resulting in thousands of individual zip files. If you are unzipping these data sets, then it is recommended that you use the Clark County Unzipper to automate the process.
As the zip files are processed, they will be restored to the directory structure employed on Clark County's host system. For example, crscl-src.zip will unzip into /gisdata/crscl/source and crscl-shp.zip will unzip into /gisdata/crscl/shapefil. Users can move the data once it is unzipped but this is discouraged for four reasons:
i. Moving around Arc/Info coverages and the associated INFO directories can easily corrupt the data.
ii. All future updates will retain the /gisdata directory structure. So if users begin moving the data around, they will have to do this each time they receive an update.
iii. Most Southern Nevada GIS users are familiar with the /gisdata directory structure. Adhering to the structure should enhance communication and coordination among users.
iv. There are plans to develop a Southern Nevada GIS Bulletin Board where users can post project files (ie. ArcView, ArcExplorer, etc.) to be shared within the community. These applications will be built on the /gisdata directory structure standard.
Unzipping data will be discussed in more detail in later sections titled Unzipping Data the First Time and Unzipping Data Updates.
II. Difference between Arc/Info and Shapefile Data Formats
Most Southern Nevada local governmental entities utilize ESRI's Arc/Info software to maintain spatial GIS data. Therefore, the proprietary Arc/Info data format is the predominant format used in the Southern Nevada GIS Central Repository. To make the data a little more accessible to other software platforms, the orginal Arc/Info data is translated into the shapefile data format and also stored in the Southern Nevada GIS Central Repository.
Realizing that most users in Southern Nevada utilize ESRI products and attempting to make data distribution as efficient as possible, the GIS Management Office only supports the proprietary Arc/Info and the ESRI shapefile data formats.
Listed below are the advantages and disadvantages of each format.
Proprietary Arc/Info Data Format
Advantages:
i. Supports annotation.
ii. Employs robust spatial model (ie. polygon and line features can be in one data set).
Disadvantages:
i. Proprietary data format.
ii. Data files are larger than the shapefile data format.
ESRI Shapefile Data Format
Advantages:
i. Published standards and therefore available to all software packages.
ii. Data files are smaller than the proprietary Arc/Info data format.
iii. The data model is more efficient (ie. faster) for displaying and selecting features on WinTel machines.
Disadvantages:
i. There is no support for annotation.
ii. There is limited internal support for spatial relationships (ie. polygon and line features are treated as two separate files.)
The two data formats can be used together. For example, a user may want to use a street centerline shape file to represent streets and at the same time, use the street centerline Arc/Info annotation file to label the streets.
III. Clark County Unzipper Software Discussion
The Clark County Unzipper was developed by the GIS Management Office using Visual Basic and a WinZip automation OCX. The purpose of the Clark County Unzipper is to automate the processing of multiple zip files. For example, when Street Centerline data is distributed, there are two files: crscl-src.zip and crscl-shp.zip. With only two files, users can individually unzip each file. However, the parcel data (ie. libpcl) contains thousands of individual zip files representing each PLSS section in the County. Unzipping these files individually would be an enormous feat.
The Clark County Unzipper will find all zip files on a particular source drive and then recursively loop and unzip the individual files to a user specified destination drive. Actual use of the Clark County Unzipper is discussed later in the sections Unzipping Data the First Time and Unzipping Data Updates.
Installing the Unzipper
The users will be supplied with a CD that contains the Clark County Unzipper software. The following steps are recommended for WinTel installations:
i. Use Windows Explorer to create a directory call c:\mytemp.
ii. Copy the file install.zip from the CD Unzipper folder to c:\mytemp.
iii. Use WinZip to extract the files from within the install.zip file. Extract the files to c:\mytemp.
iv. Through Windows Explorer, double click on c:\mytemp\setup.exe. Accept the defaults.
v. Installation is complete and an icon has been added to the Programs Menu and named Clark County Unzipper.
vi. Cleanup by erasing the c:\mytemp directory using Windows Explorer.
Uninstalling the Unzipper
If the user desires to uninstall the Unzipper software, then use the Add/Remove Programs function in the Windows Control Panel.
IV. Unzipping Data the First Time
Whether processing individual zip files or using the Clark County Unzipper to automate the process, users should extract data to the root directory for the reasons discussed above in the Overview section. A top level /gisdata and subdirectories will be created as required based on the data being unzipped.
Whether processing individual zip files or using the Clark County Unzipper, WinZip must already be installed on the computer.
Processing Individual Zip Files
i. Use the Windows Explorer to display the zip files on the CD.
ii. Double click the file to unzip.
iii. Click the Extract button in Winzip.
iv. Specific the root directory (ie. c:\) in the "Extract to:" box.
v. A top level \gisdata directory will be created and files unzipped appropriately.
Using the Clark County Unzipper
i. Start the Clark County Unzipper from the Programs Menu.
ii. From the Source pulldown menu, choose the CD drive that contains the source zip files.
iii. Press the "Display Zips from Source" button to display all the zip files on the source drive.
iv. From the Destination pulldown menu, choose a drive and root directory (ie. c:\).
v. Click "Unzip Displayed Files"
vi. A top level \gisdata directory will be created and files unzipped appropriately.
Data updates are tricker to process because there is already a root \gisdata directory (ie. c:\gisdata) containing data files. The Clark County Unzipper does not have sufficient functionality to handle file overwrites so updates must first be unzipped to a staging area (ie. c:\stage) and then copied to the root \gisdata directory (ie. c:\gisdata) using Windows Explorer.
Whether processing individual zip files or using the Clark County Unzipper, WinZip must already be installed on the computer.
Processing Individual Zip Files
i. Create a stage directory (ie. c:\stage) using Windows Explorer.
ii. Use the Windows Explorer to display the zip files on the CD.
iii. Double click the file to unzip.
iv. Click the Extract button in Winzip.
v. Specific the stage directory (ie. c:\stage) in the "Extract to:" box.
vi. A \gisdata subdirectory will be created in the stage area (ie. c:\stage\gisdata) and files unzipped appropriately.
vii. Use Windows Explorer to copy the the stage \gisdata directory (ie. c:\stage\gisdata) to the root \gisdata directory (ie. c:\gisdata). Windows Explorer may prompt for overwriting files. The users should respond "Yes to All" if appropriate.
viii. Cleanup by using Windows explorer to erase the stage directory (ie. c:\stage).
Using the Clark County Unzipper
i. Create a stage directory (ie. c:\stage) using Windows Explorer.
ii. Start the Clark County Unzipper from the Programs Menu.
iii. From the Source pulldown menu, choose the CD drive that contains the source zip files.
iv. Press the "Display Zips from Source" button to display all the zip files on the source drive.
v. From the Destination pulldown menu, choose the drive and stage directory created earlier (ie. c:\stage).
vi. Click "Unzip Displayed Files"
vii. A \gisdata subdirectory will be created in the stage area (ie. c:\stage\gisdata) and files unzipped appropriately.
viii. Use Windows Explorer to copy the the stage \gisdata directory (ie. c:\stage\gisdata) to the root \gisdata directory (ie. c:\gisdata). Windows Explorer may prompt for overwriting files. The users should respond "Yes to All" if appropriate.
ix. Cleanup by using Windows explorer to erase stage the directory (ie. c:\stage).