This map uses three data frames, each with a different projected coordinate system.
What: To decrease the amount of time required to draw the map on screen, use projected copies of the data rather than projecting "on the fly". Why: Projecting on the fly can increase the time it takes to draw the map. For this map, there are three data frames, each with a different geographic extent and each using a projection appropriate to the data being mapped. Much of the reference data (boundaries, graticule, etc.) came from the same source: the ESRI Data & Maps datasets. When we created this map, we used the data frame’s project on the fly feature, which automatically figures out how to transform the data the layers we are using into the coordinate system of the data frame. No matter how minor the transformation, it takes extra time to be compute the projection on the fly. In our case, it was taking about 25 seconds to completely draw the layout. By projecting the data to the projected coordinate system we decided to use for each data frame, we were able to reduce the draw time to 6 seconds; a more than 4:1 reduction!
How: The first step is to decide what projection you want to use for each data frame. This depends on the area and distribution being mapped. To learn more, read about map projections in the online help. The second step is to project the data used in each data frame. Follow the instructions for projecting data.
For our maps, here is what we did:
- We figured out the layout of the page and the maps that would be shown on it —- since we were copying from an existing page layout (page 138 in the Atlas of Oregon, 2nd. ed., copyright 2001, University of Oregon Press), much of our work was already done. In our case we also knew which projected coordinate systems were used on the original maps. We decided to use the same projection for two of the maps -- the Oregon State Lambert projection for the map of Oregon, and the North American Lambert projection for the West Coast map. We decided to use a different projection for the Pacific Ocean map -- we chose the World From Space projection, which is an orthographic projection.
- We then created a new personal geodatabase to hold the reference (base) and thematic (earthquake) data. We first followed our convention for storing the thematic data in one feature dataset and the base data in another. The projection used for both the base and thematic data was the North American Lambert projection. We decided not to create a new featrue dataset for the Oregon earthquakes map becuase the data used to draw it were relatively small (only the Oregon earthquakes and the counties). To speed things up, we created a new feature data set for all the data used to create the Pacific Ocean map and we projected the data into the orthographic projection of the feature dataset. This decreased the drawing time significantly, as noted above.
- For the earthquake data, we had to first use the Define Projection tool before we could move the data into our new personal geodatabase. You will have to do the same if you have data that does not have a projection defined -- ArcGIS cannot project data to a new coordinate system if it does not know what the original coordinate system is.
- Using the Project and Project Raster tools, we projected all of our data and stored it in our new personal geodatabase.
- If the data for several of your layers requires the same parameters for the Project tool, use the Batch Project tool
- If you already have a map and it's drawing slowly, go ahead and project your data and then simply open each layer’s properties, and on the Source tab use the Set Data Source option to use your newly projected data, and save your map. This is much faster than re-adding the data and re-setting the symbology.
If you would like to post a comment, please login.