Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#64 Mapping Local Areas of Interest with Quantum GIS

HACK

get the coordinates of our stream intersection on the hydro layer and on the

topographic layer. By calculating the difference, we can adjust the world file

to line up the image with the hydro layer.

The x and y offsets are approximately 112 meters and 197 meters, respec-

tively. Edit the world file stored in burro_canyon_topo.jgw and change the

(x, y) coordinates in the last two lines of the file accordingly:

16.000000

0.000000

0.000000

-16.000000

371312.000000

4015803.000000

We can now remove the topo layer from QGIS and add it back in to see the

changes. Figure 6-7 shows the same view with the adjusted topo layer. Note

that the hydro layer now lines up much better. Remember this is a hack—not

the recommended way to transform rasters to match other data. But for dis-

play/cartographic purposes, it is one quick-and-dirty way to line up the data.

In Conclusion

With a large amount of free data available on the Internet, we can fairly

quickly display an area of interest. QGIS, in conjunction with the other web

sites and tools available, makes it easy to visualize the data. Sometimes the

data are in differing projections and/or datums, but with a little clever

manipulation, you can always torture it into submission.

Figure 6-7. After manually adjusting the world file