Allison Perch

Allison Perch

Lab 4

Georeferencing Lab

Questions:

1.Georectifying an image involves taking two maps that are the same and using points to line the map up. For instance, in this lab, a map of a very specific part of North Carolina was used. Using Google Earth, you can pinpoint a landmark on your specific map. Then, using ArcMap, you can find this same point on the basemap of North Carolina. After the image of the map has been added to the basemap, you can use the “Control Points” tool to find a point on the image that matches a point on the basemap. By finding combinations of points that match up, the image will adjust itself so that it fits well over the basemap.

2.This technique can be used in the future to calibrate between various maps so that they are more accurate and similar. For instance, if one map is missing certain features that another map contains, the maps can be georectified onto one map so that the new map gives a fuller picture of the area. When researchers map a new area or discover new features in an area, they can use georectification to add their features accurately to an already existing map.

3.To georectify a map, you can use the rectify button on the georeferencing toolbar to permanently change the map, or you can use the Warp tool. The georeferencing tool bar method permanently changes the raster dataset so that a new map is saved. You can also save the transformation in a new file using the Update Georeferencing command. For this lab, we used the rectify button on the georeferencing toolbar, which permanently changed the image so that it would fit on the basemap.

4.As I added more points, the RMS became larger. This is because the image and the basemap are not entirely the same, so while a point on the image may match up perfect with a point on the basemap, when a second point is added, the map may have to modify slightly so that each point can still be correct. Therefore, the RMS becomes larger because there is more residual as more points are added.