NR 322: Editing Spatial Data Jim Graham Fall 2008 Chapter 6

Digitizing Spatial Data We are creating a representation of objects on the earth What accuracy is important? How did we determine their position? How will the data be used?

Accuracy Accuracy: How closely the data matches truth What accuracy do we need to maintain? Typically you want to collect data that is twice as accurate as will be needed to allow for conversions to decrease the accuracy.

Data Collection How was the data collected? –GPS –Topographic Map –Surveys to benchmarks –“About here” on a satellite photo Each step has an effect on accuracy: –Instrument –Digitizing –Transforms (projection)

How will the data be used? Maps at large extents, low resolution? Maps at small extents, high resolution? Analysis?

Digitizing Process ArcCatalog: –Create the Shapefile ArcMap: –Add the Shapefile (or Coverage, or GeoDatabase) –Add attribute fields –Start Edit –Add points, polylines, polygons –Add attribute values –End Edit ArcCatalog: –Add Metadata

Create New Shapefile In ArcCatalog: –Select New -> Shapefile –Select the type of file –Define the spatial reference (coordinate system) to match the raster –Z adds an elevation –Don’t worry about M yet

Questions to ask before editing Points: –What part of the feature to identify? Adding Polylines –What level of stream? –What level of road? Adding Polygons –What level of resolution? –How small a feature to include?

Editing Points Adding: –Tool: Sketch Tool –Task: “Create New Feature” –Target: Matches Point Layer –Click to add points Edit/Delete: –Tool: Edit Tool –Task: NA –Drag to move points –Right-click to delete points

Editing Polylines Adding Polylines: –Set “Snapping” –Tool: Sketch Tool –Task: “Create New Feature” –Click to add points –Double-click to end polyline Editing Polylines: –Tool: Edit Tool –Task: Modify Features (watch this) –Drag to move vertices with special cursor –Right-click to delete vertices

Editing Polygons Adding Polygons: –Set “Snapping” –Tool: Sketch Tool –Task: “Create New Feature” –Click to add points –Double-click on start vertex Editing Polylines: –Tool: Edit Tool –Task: Modify Features (watch this) –Drag to move vertices with special cursor –Right-click to delete vertices

Editing Metadata Select the file in ArcCatalog Select “Edit metadata” Enter all 200 fields! Fill out: –Identification: required fields –Data Quality –Spatial Reference –(not required for Lab 7!)