After exporting the GPS data to a GIS format, check the data in a GIS program for quality and completeness. Incomplete editing in the post-processing step and any exporting mistakes need to be identified and corrected before the GIS dataset is documented. Combining of data with pre-existing datasets or further spatial analysis may need to take place during this step.

Add the exported datasets into a GIS program (like ESRI's ArcView or ArcMap) with other GIS data collected in the GIS Inventory step to check for projection and datum problems. READ MORE >>

All of the data should align properly. If you GPS datasets are in a completely different realm of the earth, then the GPS data is probably in a different projection. If the GPS datasets are 10 to 50 meters off or look shifted, then the problem may be different datums. Reexamine the export methods from the last step to correct any data projection and datum problems.

In cases where high positional accuracy needs to be confirmed or tested, the National Standard for Spatial Data Accuracy (NSSDA) is a good place to start. The NSSDA describes a way to measure and report positional accuracy of features found within a geographic data set. You can run tests on your current datasets or utilize reports of accuracies for similar GPS units and condtions generate by several federal agencies. See GPS Unit & Project Needs Assessment Links section for more details.

Make sure any erratic or duplicate positions have been edited out and all arcs are properly closed and connected. READ MORE >>

Editing positions is covered more thoroughly in the Post-Processing step. Some individuals prefer to complete or do all of the position editing once their data is a GIS format and software. Most GIS software programs allow for easier identification of arcs not properly snapped together or snapped to intersections. Editing may take some time because the user will need to zoom into and around the dataset at a fairly large scale (~1:2000) to spot inconsistencies. See an example of a corrected line error and a corrected polygon error.

Review and edit the attribute tabular data. READ MORE >>

Additionally, some manual data entry maybe be required if the attribute collection method included taking hardcopy notes about features while in the field. Make sure field entries are standardized, complete, and useful. Think about having an attribute that makes map symbolizing easier if your dataset does not already include one. Lastly, if the dataset is going to be merged or combined with data from a different source, make sure the attributes are identical before creating a single dataset and add an additional attribute to keep track of the source of each feature.

Perform any advanced data manipulation. This could include any data combining with other datasets, creating hotlinks to photos, or performing a spatial join in order to trim features or add attribute information.

Once the dataset is finalized, complete your GPS project by documenting all of the finalized datasets with metadata and the project itself.

Altering data - Whenever the topology of a feature is altered (e.g. vertex deleted in a shape file or in building/cleaning a coverage), any units such as length and area attributes carried over from the GPS export process must be re-calculated. Unit values exported in the GPS software may not match the final unit values in an edited GIS layer.

Combining Data - When combining GIS datasets, remember that the attributes tables usually need to match exactly in order for the attribute information from all input datasets to make it into the combined dataset. The features usually combine properly, but look carefully at the attribute tabular data to ensure the fields are complete and standardized. If combining data from two different source scales (ie. GPS data with heads-up digitized data) create an additional attribute to hold information about the source of each feature. (Example. Add an attribute field called "Source" and populate each feature with "GPS" or "Heads-up". Alternately, add an attribute called "Source Scale" and populate each feature with 1:2400", "1:12000", etc.)

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