ABSTRACT
The Planning Data Services Bureau of the Georgia Department of Transportation has a two-fold GIS mission. They need to maintain and update their road characteristics database (RCFILE) and produce publication quality maps for each county in the state. Using the basemap's route features, which have been calibrated to the intersection level, a number of cartographic products can be produced in a semi-automated fashion. The RCFILE uses a linear referencing system, therefore dynamic segmentation can be used to map the road surface types and bridge locations. Annotation subclasses for route numbers and road names are generated from the route feature attributes rather than individual arc attributes, thereby reducing the amount of editing. A unique set of problems arise, however, from the integration of dynamic segmentation into the cartographic production process. In addition to an overview of the cartographic production techniques used in ArcInfo, the solutions and work-arounds necessary to mitigate these problems are discussed.
INTRODUCTION
The Georgia Department of Transportation (GADOT) has long been responsible for, among other things, two very important tasks: (1) the maintenance of a road characteristics database, and (2) the publication of up-to-date road maps. The city and county map series published by the Planning and Data Services Bureau of GADOT have been relied upon by state and local government as a source of information and a map base upon which to build. Historically, these maps were produced by GADOT using manual cartographic techniques. Maintenance of the road characteristics database (RCFILE) for planning and inventory purposes was a concurrent but separate endeavor. In order to meet federal, state, and internal requirements, GADOT contracted with the Government Information Services Division (GIS Division), located at the University of Georgia, to produce a GIS map base which would serve both the cartographic and planning needs of the Bureau.
The initial data conversion to create the map base from the GADOT hard copy maps has been completed, and the GIS Division is currently in the process of updating the maps using digital orthophotography. One of the processes involved in building and updating the GIS map base has been the creation of a route system calibrated to the intersection level. The route system allows for dynamic segmentation modeling for both planning and cartographic purposes. This paper describes the ways in which ArcInfo's dynamic segmentation capabilities can be integrated into the cartographic production of publication quality road maps.
BACKGROUND
The city and county map series were originally converted from hard copy Mylar maps, using large format tablet digitizers. During this stage of the data conversion, city, county and state maintained roads were tagged with a unique ten digit code, the RCLINK number. This number links the arcs in the database to GADOT's RCFILE. A route system was then built on top of the arcs, based on the RCLINK number. This route system has been calibrated based on milepoint data, stored in hundredths of a mile in the RCFILE. Calibrating the roads database to the intersection level for city, county and state roads, though very time consuming and somewhat tedious, will ultimately produce a route system which meets the accuracy requirements for the planning and cartographic needs of the Bureau. (for more information on the RCFILE and route building processes see Higgins, S., Esri Conference Proceedings 1996, Paper# 290; and Price, J., Esri Conference Proceedings 1996, Paper# 141)
During the data conversion process, a number of ancillary data layers were also created. These layers include hydrology, political boundaries, oil and natural gas pipelines, transmission lines, railroads and general cultural information. Currently the GIS Division is updating the statewide road and hydrology layers using digital and hardcopy 1993 NAPP photography as well as GPS data collected by GADOT. The other layers are also being updated, based on inventories performed by GADOT on a five year cycle. These layers, in conjunction with an annotation layer and the roads layer, are used to produce the final cartographic products published by the Bureau. These products include 1:31680 and 1:63360 scale black and white county maps, and a city map series produced in black and white at a variety of scales. GADOT publishes their city and county map series in black and white to keep down production and reproduction costs, as these maps are used by a very large number of state and private organizations.
The following sections describe three ways in which the route model and dynamic segmentation has been used to automate or enhance cartographic production:
AUTOMATED LINE SYMBOL GENERATION: ROAD SURFACE TYPES
One of the challenges of producing DOT maps using manual cartographic techniques, has been the accurate and up-to-date depiction of changes in surface type along a given road. Using the dynamic segmentation model implemented in GADOT's GIS map base, changes in surface type can be depicted "on the fly." When the RCFILE, which contains data regarding surface type, is updated, these changes can be easily mapped along the routes. Once an event table has been created, and the event source defined, the changes in surface type can be mapped simply by using the EVENTLINES command in ARCPLOT. This command allows the user to draw the events to the screen (or into a metafile) without altering the topology of the existing roads coverage. The events are simply mapped along the route according to their relative position along the linear referencing system set up and calibrated during the route building procedure. In a perfect world, this command could be used to produce the surface type symbology for final cartographic production. This would allow for the publication of updated maps in a more timely manner than has been historically possible
In reality, the generation of surface types for publication quality maps requires some editing. In one scenario, there are certain roads on the published maps which are shown using a smaller line weight than most. These roads will usually a fall within a congested or otherwise cartographically crowded area. Obviously the criteria used in cartographic decision-making will not always be coincident with the types of information stored in a planning and inventory database. In another scenario there may be gaps in the database, which will in turn leave gaps in the symbology used to depict the surface types. Clearly the reliability of the associated database is at issue here. Since the database stores state-wide information for a road network calibrated to the hundredth of a mile, some margin of error is nevertheless to be expected. In any case, one solution to this problem is to use the EVENTARC command to create a new coverage from the event data. This coverage can then be edited by hand to accommodate the unique situations where a road is not symbolized according to the surface data stored in the road characteristics database.
Another situation which may arise concerns the drawing order of routes in ARCPLOT. In most cases, a solid fill road pattern should opaque or mask intersecting arcs with an open fill pattern. Even when using a lineset which contains masking open fill patterns, this can easily be controlled by reselecting the solid fill arcs and drawing them last. Every once in a while a situation will arise in which a single route needs to both overlay and underlay a given line type. Clearly a simple reselect will not achieve the desired cartographic results. This is the case shown in Figure 1. The divided highway running northwest to southeast flows under a solid fill road at point A, and over the same road type at point C. In order to draw these arcs in the proper order, small subsections of the arcs have been hand selected in ARCEDIT and PUT into a new coverage. This new coverage is drawn as the last step in the sequence of commands used to draw the road symbology.
Figure 1
AUTOMATED POINT SYMBOLOGY GENERATION: BRIDGE LOCATIONS
The importance of the accuracy level to which the route system has been calibrated becomes very apparent with point data. A database calibrated at the intersections of all state, county, and city maintained roads, is more likely to yield good results, than one calibrated only at the intersections of state maintained roads. For example, signalization events such as stop signs or flashing beacons, will be mapped perfectly along the route, if the route system is calibrated at every intersection. If the routes have been calibrated to a lesser extent, the likelihood that a stop sign event will land between two intersections is much higher. As such , a well calibrated route system and a good database should allow for "on the fly" mapping of point events during cartographic production.
The reality, once again, is not so perfect. A variety of factors, including the scales at which data layers are captured, can create problems which will require the creation of an editable coverage. During the original data conversion stage of the GADOT map base project, a decision was made to capture the hydrology from 1:24,000 USGS 7.5 minute Mylar separates. The GADOT map base from which the roads were originally captured is published at 1:31680. As a result, bridge locations, mapped using the EVENTMARKERS command in ARCPLOT did not always fall precisely over their associated hydrology.
The solution was to use the EVENTPOINT command to create a separate coverage containing the bridge locations and types. In doing so, the angle variable which automatically rotates points so that they are aligned with the route on which they fall, is lost. For many point events this would not be a problem, but in the case of bridges, their alignment with the road is an essential cartographic standard. A second step becomes necessary to realign the bridges with the roads, so that each and every point does require hand editing. Using a simple SHOW function, the angle of the underlying arc can be captured and associated with the bridge point marker (see Appendix 1 for a simple AML to do this).
Another potential problem with producing publication quality maps concerns the "special case" situations which arise where the bridge symbology may need to be different (e.g. larger or curved) to accommodate cartographic standards. After some initial testing, it was discovered that using a standard set of bridge symbols to accommodate the myriad possibilities which might arise was inadequate. The bridge at location B in Figure 1 is an example where an oversized symbol was required to span the river and railroad running below. The railroad's moveable span bridge at location D also had to be added to the database manually, because it did not fall on a road, and thus was not accounted for in the RCFILE during the generation of the bridge points coverage.
Even considering the scenarios described above, the ability to dump the locations of bridges into a point layer using dynamic segmentation does cut down on the total amount of labor required to capture and adjust the data necessary for cartographic production.
GENERATING ANNOTATION USING ROUTETEXT
The ROUTETEXT command in ARCPLOT will add annotation text on the fly to route features, offsetting and placing the text at specified intervals. The advantage to using ROUTETEXT over ARCTEXT is that routes made up of multiple arcs will only be labeled at the specified interval. As is the case with the other route related commands in ARCPLOT, the results from ROUTETEXT are reasonably good for most uses. In order to meet the cartographic standards required for publication, however, a separate coverage must be created and edited. Using the ANNOCOVERAGE command in ARCPLOT, annotation text can be dumped into a coverage which may then be edited in ARCEDIT. This also allows for incidental quality control. Although a wide variety of quality control measures are undertaken throughout the map base update and route calibration process, the use of routetext provides an additional check. If the user editing the annotation notices that the road number generated from the routes does not match the road number on the inventory sheet, the discrepancy will be noted and the routes and/or annotation can be corrected.
COMMENTS AND CONCLUSIONS
One of the biggest challenges in creating publication quality cartographic products for GADOT has been developing a digital product in ArcInfo which mimics the cartographic specifications achieved using manual cartographic techniques. A number of work-arounds and innovative solutions were required to achieve some of the standards. The solutions associated with the use of dynamic segmentation have been discussed in this paper. In addition to these, a wide variety of cartographic tricks in ArcInfo were acquired during the development of the final product. (It was decided that a more thorough explanation of these is best suited to the poster session environment) Once an acceptable product was created, however, the code used to produce the maps was in place. AML applications have been created, standardizing and automating the map base updates and cartographic production. These applications have been delivered to GADOT, where they are currently being used to make final changes to the map products, before they are sent to the printer. In the future, GADOT will be able to use these and other ArcInfo applications to maintain and update their digital map base in conjunction with the road characteristics database. With the help of dynamic segmentation, the production of city and county maps at that point in time will require a great deal less time and effort than in the past.
APPENDIX 1
Sample AML to get the angle of an arc and rotate a label point to match the underlaying arc. This piece of code was written to align bridge markers to their corresponding road arcs.
This is run in ARCEDIT
editcover bridge_points
editfeature label
select all
&setvar .num = [show number select]
&setvar .j = 1
cursor open
&do &until %.j% = %.num% + 1
cursor %.j%
&setvar .xy = [show label [show select 1] coordinates]
editcover roads
editfeature arc
coordinate keyboard
select
%.xy%
&if [ show number select ] = 1 &then
&do
&setvar .ang = [show arc [show select 1] orientation %.xy%]
editcover bridge_points
editfeature label
select all
cursor open
&type [quote Calculating the angle for bridge no %.j%]
cursor %.j%
calc $angle = %.ang%
&end
&else
&type [quote No arc selected, skipping bridge %.j%]
&set .j = %.j% + 1
&end
Kate Landis
GIS Program Coordinator
Carl Vinson Institute of Government
University of Georgia
201 N. Milledge Avenue
Athens, GA 30602-5482
Telephone: (706) 369-6062
Fax: (706) 542-6535
E-mail: kate@gis.lislab.uga.edu