August 11, 2008


Into the Wilderness

I am planning a camping trip with my daughter. I grew up understanding that the term camping was a word reserved for the act of wilderness hiking. Our family made a distinction between hiking and lesser forms of camping like car-camping, which is prone to result in too much stuff and too little place to pack it. I later learned that camping might also apply to vacationing in a cabin in the Northeast. In my youth I would often hike a week at a time in the national parks of Washington State and never see another person; deer, bears, mountain sheep, chipmunks and mosquitoes, yes, but no other people.

In planning this short overnight hike with my daughter I am contemplating the minimum amount of gear I will need to enjoy the trip. I am a firm believer that the key to camping is comfort! It is a family creed.

As with many things in life, the idea of carrying everything you need to be comfortable up a steep mountain can create opposing requirements. If you pack too much gear you won’t be comfortable carrying it. If you don’t carry enough gear you might be miserable without it.

Packing GIS data for the CAD wilderness is what MSD is all about. There are many different ways to organize data in an AutoCAD file. There are also various strategies to associate attributes with entities. These include attaching external databases, linking entities together and leverage block attributes for polygons and lines as well as point feature, adding simple text. Extended Entity data is another way to add additional information in the dwg file, most of these lack a user interface all have significant limitations. Xrecords, their container objects, the Extension Dictionary and the Named Object Dictionary, are the modern mechanism for storing non-graphical data and attaching them to entities in AutoCAD.

The Mapping Specification for DWG (MSD) is ESRI’s response to evolving technology. Leveraging these methods of storing information in a well defined and consistent way allows GIS information to be encoded directly in the drawing without resorting to the pitfalls of implementing and supporting AutoCAD custom objects that are powerful yet ambiguous additions to the DWG/DXF file and are impossible to use without the application that created them.

MSD allows ArcGIS users to share feature class data, feature class organization, and attribution with plain AutoCAD users. Likewise standard AutoCAD users can create rich GIS content with attributes for future use in ArcGIS and their own AutoCAD application needs, knowing the resulting data created in AutoCAD will be directly usable in AutoCAD and ArcGIS. Most importantly MSD allows CAD draftsman to create standard AutoCAD entities using their existing CAD standards to create this data. MSD uses standard CAD entity properties to define the criteria for inclusion in a GIS feature class and therefore uses rather than replaces existing workflows.

The MSD specification is published here in the CAD Section of theArcGIS 9.3 online help.


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