Surveying GIS: The Data Tsunami.
One of the things the digital electronic age has done for us is to make massive amounts of information and data available on the desktop at the click of a mouse. Storage requirements for that data have leaped from megabyte capacity to petabyte needs in barely a decade—and in the process spawned the term “Data Tsunami.”
Everyone who accumulates large volumes of electronic digital data over time needs the proper tools to manage it. The surveying and mapping community is no exception. We, too, have data management needs, some of which are both special and spatial. Fortunately for us, there are powerful tools available to address the challenge. ArcGIS is one such tool.
In the last installment (April 2003) we examined the construct of the geodatabase and viewed some data and its properties in ArcMap. As discussed, ArcMap is one of the three component parts of ArcGIS. The other two elements of this power suite are ArcCatalog and ArcToolbox. These are the tools of data management.
ArcCatalogThe desktop icon for ArcCatalog looks like a small file cabinet with a “beach ball” globe in the drawer. Clicking on it opens a window that resembles Windows Explorer. The left frame is called the Catalog Tree. The Catalog Tree displays and allows access to the contents of the Catalog.
The “Connect folder” command is available from the “File” menu or from the icon, the small yellow arrow with a globe on the menu toolbar. It operates much like the “Map Network Drive” command in Windows Explorer and largely controls what appears in the Catalog Tree. It also allows the user to connect to RDMS and SQL data sources.
The right frame has three tabs: Contents, Preview and Metadata.
The Preview tab can be toggled between the Geography view and the Table view using the arrow in the box at the bottom of the right frame. In ArcCatalog there is no need to add or remove layers in Preview. The user can simply move through and examine everything in the Catalog without creating a project (.mxd) file, as shown here.
As the user navigates through the data in the folders, he can use the “Create Thumbnail” button to make “thumbnail” views in the folder for easy identification later. This data management approach can be advantageous to the surveyor because it allows him or her to co-mingle various data types by job or project folder. CAD files can reside with GIS data and any other file types associated with projects. The user can assemble the folders in any order he or she chooses but still has the freedom to access or move any of them to, from or between projects.
The Metadata tab is truly innovative. It contains developed models called “Stylesheets” for viewing and creating metadata.* The ESRI Stylesheet is the default. The FGDC (Federal Geographic Data Committee) Stylesheet is a framework that auto-selects all available data defined by the FGDC standards for inclusion. The innovative part is that when the user activates the Metadata tab, ArcCatalog will create metadata if it does not already exist. ArcCatalog metadata is stored as XML (Extensible Markup Language) and displayed as HTML (Hypertext Markup Language). The Metadata Toolbar assists the user in creating and editing metadata.
Choosing the FGDC stylesheet tends to create larger metadata files. The Metadata Toolbar is located to the right of the Stylesheet window. This toolbar houses the buttons used for creating, updating and editing metadata.
Important! Precision is always a concern for surveyors. Not only is it important to deal with this issue in the metadata, but it is even more important to address it in the data. Most surveyors are familiar with the concept of significant figures. So are computers. And like surveyors they must first be instructed to be aware of the difference between 1,846,234.5 and 1,846,234.49876.
Datasets in ArcCatalog can be created and stored in either double or single precision format. Double precision storage of course requires more space. Single precision is the default. So, it is incumbent upon the user to determine the need for and set the option for double precision. Precisions are set using ArcToolbox.
ArcToolboxThe desktop icon for ArcToolbox is, prosaically enough, a red toolbox that looks much like those some of us have in our garages. This little red toolbox doesn’t have any wrenches or screwdrivers inside. It has hammers. Expanding any folder “opens” the virtual toolbox and displays a variety of tools and “wizards” represented by a hammer icon. The hammer is indeed an apt metaphor for the power of these data management tools.
There are four groups of toolsets in ArcToolbox:
- Data Management Tools. These tools are designed to assist the user in organizing and managing datasets. It differs from ArcCatalog in that the user can modify datasets as well as arrange them.
- Analysis Tools. These tools contain the ArcToolbox geoprocessing functions. Datasets can be merged, buffers created and various statistical analyses can be performed.
- Conversion Tools. These tools are the surveyor’s friend. With these conversion tools, the user can convert to and from many of the industry standard CAD/GIS formats very easily.
- My Tools. My Tools is a placeholder for a “custom” toolset the user creates from the other toolsets or from Visual Basic scripts.
The Projections folder is a good example. The ArcToolbox Projection Wizards are very easy to use. They all have easy-to-follow dialog boxes, allowing the user to set or change the projection of a dataset.
Projection tools, like some other functions, are embedded in more than one toolset or module. This is one of the strongest features of ArcGIS. The developers have placed or grouped tools in locations that follow the logic of many task sequences.
When we toured ArcMap, we looked at how it handled CAD datasets. Let’s “close the loop” by taking a look at ways to use GIS data for CAD projects with the aid of the data management toolset.
It is often useful to display existing data layers as background in CAD drawings. ArcGIS performs tasks like these with great efficiency in a simple, straightforward manner. Under the “Conversion Tools” set, the user selects an existing file format and a desired file format in one simple dialog box. That’s it!
In this example, we’ll choose “Shapefile to DXF.” The small dialog box appears. Click the File folder icon in the upper box to navigate to the desired Shapefile and select it. Then set a path and name your DXF output file. Click “OK.” That’s it! There is also a “Batch” option that allows the user to convert multiple files.
As usual, there are a few caveats one needs to consider when something is simple and easy. In this case the user needs to be mindful of the correct and proper projections and coordinate systems to achieve the desired result. Aside from that, the conversions routines are very user-friendly.
What I have presented here is a very brief overview of a complex, comprehensive and extremely powerful GIS toolset. In future works we will probe deeper into the ways these tools can be used for the benefit of the surveyor.
* The user may also develop his own style sheet.