Stack Symbols ArcView extension was developed by WESTON to automate the repeated mapping of very large three-dimensional environmental data. Stack Symbols extension demonstrates an innovative use of graphics for data symbolization using Avenue and customized font-set. Use of the extension reduced the task completion period from 4 persons a week (160 hrs) to two persons a day (16 hrs), along with aesthetically pleasing and understandable maps. The paper describes the process of developing Stack Symbols and its associated tools in ArcView GIS, that would help environmental agencies implement more communicative maps with significant time-savings.

The project currently holds more than one million records stored in Microsoft Sequel Server database and is still growing. The data is arranged with the samples as the basic unit of information, uniquely identified by a Sample_id. Generally, each sample is taken at a specific depth interval. Depth intervals of the samples are not consistent throughout the dataset. At a single location total number of samples could vary from 1 to 48 with depth intervals that are often not consistent.

Every unique location (in Plan view ) was identified as Location_id. New samples were added to the dataset almost every day. Data set was updated twice a week. ArcView created event themes with locational information coming directly from the Access database.

Client had specifically requested paper maps for reporting the sample results, which had to show data in an aesthetically pleasing and easy to understand format.

Generating the maps that displayed all the results in postings boxes was a very time consuming exercise. It took about four analysts working full time to finish all the maps in a week. By the time the maps were done, they had to be updated again because the data had changed.

The default ArcView symbol sets could not accommodate such a large number of sample types. The results had to be posted with information that could be coming from multiple fields. The shear size of the data that had to be posted could not be accommodate in the weekly schedule.

Manual generation of postings map was very time consuming. Also once the maps were created they could not be reused in any way, because the data was already old, and posting boxes were done manually anyway.

The fonts would have same point of reference but different horizontal bands that could be colored to display result values (see figure)

Hence we developed a new custom font type called stacked bar symbols. Macromedia Fontographer version 4.1 was used to design and generate the new True Type font. A composite marker palette was created in ArcView using the characters from this new font. Twenty-one separate characters formed the basis for each bar in the stacked symbol representation. Character sizing and placement in Fontographer was critical to the proper display in ArcView, and special care was taken to ensure that characters overlaid one another cleanly.

When we tried using the fonts to symbolize the data, we realized that we could not use them directly.

This is when we thought of creating symbolized graphics on top of the location theme features. These graphics were to generated using stacked bar symbols font set. The challenge was to make these graphics look and feel like single symbol for each location_ID (NOT sample_ID). At the same time these stack symbols had to be easy to move around, and intelligent enough to know their respective Location_ID and all the Sample_Ids that formed them. We achieved this through ObjectTags.

1. Departmental Cartographers who would use the ArcView project file, and could perform some of the tasks manually. It gives them more flexibility in developing the maps.
2. Environmental Engineers are the End Users who are supplied with the Stack Symbols ArcView Extension. Most of the data processing tasks as run in the background thus minimizing unnecessary complexity and confusion.

To generate Stack Symbols these 8000 records are further processed:

1. Depth Intervals for each location_ID are ranked and used to populate a new field called "Rank".
2. Locations with total number of samples greater than 21 are flagged in a new Boolean field named "RankAbv21"

Whenever a new project is created for Stack Symbols, the ArcView palette containing the Stacks font set is saved with the ArcView project so that it would always be available in the memory when the project is loaded.

Finally, Stack Symbols are generated for each location_ID with topmost stack showing results of sample with Rank value 1. The color of the stack symbol is determined by a logic that depends upon the depth and result value of a sample.

Once the stacks are generated the they are resized, using customized tools that would increase or decrease Stack Symbol sizes.

Overlapping stacks are moved around little bit to get a more legible and aesthetically pleasing map. Automated line generating tool draws a line between a stack and its source location. This helps minimize the confusion about the source location for a stack symbol when it is moved.

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