GIS Import Options: Pros and Cons
AutoCAD® MAP gives the user two options on importing GIS data. For this article, we’ll use ESRI Shape files as an example. Your options are to link the data through Data Connect, or Import through Planning and Analysis Workspace. Each method has its advantages and disadvantages; the key ones will be discussed here along with instructions on how to do both.
There are similarities to importing and linking. Each can be displayed almost the same way, and the data can be accessed depending upon how it’s imported. However, the question to ask is which is more important to your project: the data or the entities.
Linking Via Data Connect
Data Connect is the method to linking to data such as raster files, shape files, ArcSDE, and many others. One advantage of this is by linking the data, any modification to the data means your drawing is automatically updated as well. You can even use MAP to modify the data. That could be a disadvantage if you make a change that you didn’t intend including erasing a feature or changing data in a data table.
There are other ways of visualizing the data not available to standard AutoCAD entities. This includes creating unique styles, filters, and thematic rules.
For instance, what if we have a variety of zoning districts in a city, and we want to show the various districts in different colors? (I will be using the City of Bismarck GIS data in all of the examples.)
First we need to link the data via Data Connect. Click on the Connect button on the Home tab or Data in the Task Pane (Display Manager tab). See Figure 1. From there, highlight what kind of connection you want (see Figure 2). In this case, I have the Zoning Districts imported, but they all look the same. Short of clicking on each one, I have no idea what each zone is.
What I can do is create a theme that will give each zoning district a unique color. Click on Style in the Task Pane (right- clicking on it will give you a lot more options including editing the style). Click on New Theme (see Figure 3) and from there pick the Property you want highlighted. In this case I want ZONE_. It gives me both a minimum and maximum value. For the style range I can pick whatever beginning color and ending color I want. As shown in Figure 4, I now have a better idea of what each zone is. If I don’t like the color of a specific zone, I can always change it by going back to the Style Editor.
If I decide I don’t need one set of data, I can merely click it off and it disappears, much like turning off a layer.
Another advantage to linking is because the data is not part of the drawing, the CAD file is small and therefore reacts quicker than if you import them as CAD entities.
Another plus to linking is no matter how far you zoom in or out, with the features linked as symbols (such as manholes or gate valves), the size shrinks or enlarges respectively. Note, too, you can add CAD symbols to your style library.
Feature lines can also be shown using any CAD linetype loaded in the drawing, and you can also set the width which also shrinks or enlarges as you zoom so the linewidth appears the same no matter how far out or in you zoom. Printing is the same.
Importing as CAD Entities
The main reason to import instead of linking is for smaller projects within the GIS system. For instance, I’m working on a site plan within a single block. I don’t need access to the entire city data, and I’m more interested in where things are located and not necessarily the attached data (although that can be brought in as well during import). I also want to be able to eliminate entities I don’t need from the drawing.
With import you can also bring in a small portion of the data instead of the entire area.
First you need to determine your area of interest. In this example, I used an aerial photo, and drew a rectangle around the area (see Figure 5).
The first set of data I want to add are the watermains, gate and fire hydrants. In the Planning and Analysis workspace, click on the Insert tab and click on Map Import. A dialog box pops up asking for the location of the data and its type. In this case, I want to import ESRI Shapefiles (Figure 6).
I click on each shape file I want to import and click OK.
The next dialog box is the most important. Here you can choose the import coordinate system if it’s different from the data (such as converting from International feet to meters). You can change the layers to whatever standards your company uses. You can also choose to include the data such as watermain type and size, but depending on your uses, it’s not required. The last option, Points, allows you to pick any symbols you normally use.
Note: If you’re bringing in any closed polygons, click on Import polygons as closed polygons. If you don’t, the polygons will come in as MPolygons.
Be sure to click on the Define Window button located in the Spatial Filter area in the upper right of the dialog box before you click OK. Otherwise all of the data will be imported instead of the area you want. When you click on the Define Window icon, AutoCAD asks you to choose two corners for the import window. In my case, I merely pick the lower left and upper right of my rectangle.
AutoCAD brings in all entities that cross the rectangle (see Figure 7), so you may have to trim whatever falls outside your area. The nice thing about importing is that trimming or erasing the data will not affect the original data.
The disadvantage is if any of the original data is updated, your drawing will not reflect it.
One key to good productivity and, in the end, the ability to present good information for the client is having options in accessing that data. This happens by asking the right question at the start: How will the data be used?
Andra Marquardt is a Professional Land Surveyor in the State of North Dakota, and has worked for Toman Engineering Company since 1997. She has used AutoCAD beginning with Version 9, and currently uses the latest version of AutoCAD Civil 3D.