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# PCCC GIS I Exercise 2 (AV9.1) - Locate your car with GPS, map it with GIS v2, Apr 2007 - page 10 / 31

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Optional NOTE: Now, and in most cases, you want to leave the “include positions that are…uncorrected” box unchecked (red arrow above left). However, sometimes it may be difficult or impossible for you to differentially correct data. In these cases, checking the “uncorrected” box allows you to export your “uncorrected” data into a GIS system. This is NOT a preferred alternative, but rather a last resort.

• Click OK on the bottom of the Export Setup Properties window (blue arrow above left).

# The Export window returns (above right):

• Click OK on the upper RH button (green arrow above right).The shapefile will now be transformed from a Trimble format into an ESRI point shapefile and saved to your group *_GPS folder as point.shp. Scroll to your folder and confirm that the shapefile is there.

NOTE: For Steps 6 and beyond, students work separately Step 6 - Open a new, empty map and set projection to NJ State Plane, NAD 1983 Discussion: Before you bring your GPS data into Arcview, you will learn an important task of the GIS practitioner: understanding and changing projections (coordinate systems). This is an important skill, because GIS data come from many different sources, often in different coordinate systems, and the ability to change a variety of different data into one common projection on one map is essential to the GIS practitioner. Recent versions of Arcview (8.x, 9.x) are capable of automatically performing a change of projection for shapefiles in one coordinate system (e.g., Geographic [latitude/longitude] coordinates to another (e.g., State Plane).

Projections are necessary because they allow for defined, systematic distortion that is created when you try to “map” a 3D world on a 2D, flat surface. Different projections emphasize directional accuracy at the expense of size (e.g., the huge size of Greenland on a Mercator projection, which preserves angles but not size), or vice versa. There are always tradeoffs, because it is literally impossible to perfectly replicate a 3D world on a flat, 2D surface.

In this step, you will first learn how to define the projection of the Map view to NJ State Plane (feet), North American Datum (“NAD”) 1983. Then you will add lat-long TIGER data that will automatically be re-projected into State Plane coordinates. Procedure:

• Open ArcMap (Start > Programs > ArcGIS > ArcMap

• At the window prompt, select “New empty map” (below left):

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