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GPS Best Practices

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zora
19 diapositives · 329 Views · Feb 18, 2014

Project Planning James Stein NPS Historical Documentation Programs Cultural Resources GIS GIS and Data Management Conference April 1, 2008. Four Steps in Project Planning. Decide on the purpose of the survey Write a project description Decide on level of accuracy

#cultural resources #gis practices #survey accuracy #data dictionary #data collection
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GPS Best Practices
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  1. GPS Best Practices: Project Planning James Stein NPS Historical Documentation Programs Cultural Resources GIS GIS and Data Management Conference April 1, 2008

  2. Four Steps in Project Planning • Decide on the purpose of the survey • Write a project description • Decide on level of accuracy • Determine what information is already available

  3. Purpose of the Survey Baseline Inventory Application Survey • Many types of features • Few attributes • Limited types of features • Many attributes

  4. Purpose of the Survey • Most GPS projects are combination surveys • Data dictionary can describe many features, yet capture detailed attributes

  5. Project Description and Research Questions • A project description explains the purpose of the project and outlines research questions • Focuses survey efforts on collection of required features and attributes Example Research Questions What is the extent of storm damage to the cultural landscape at the Hermitage historic site? Which area received the most damage, and which species of tree? What will be the cost of clean up to the historic landscape? Target area for maintenance

  6. Level of Accuracy • Purpose of the survey determines the level of accuracy required • Smaller scale data may resolve your research questions

  7. Level of Accuracy 1:250,000 scale USGS 1x2 degree series +/- 250 meters 1:100,000 scale USGS 30x60 minute series +/- 90 meters 1:24,000 scale USGS 7.5 minutes quadrangle maps +/- 12 meters 1:2,000 scale site plans and tax parcel maps +/- 5 meters (varies) GPS (mapping grade) +/- 1 meter GPS (survey grade) +/- 10 centimeters Laser transit boundary line survey +/- 5 centimeters

  8. Available Information • Geographic information is available from many sources • Digital base data may already exist for your study area • Prime sources include the Census Bureau and USGS Alexandria Cemetery plan 2004 Alexandria Cemetery plan 1892

  9. Data Dictionary • A data dictionary is a list of features to map • Serves as a guide to surveyors in the field • Data dictionaries consist of features and their attributes Capturing too much data can result in complex maps which are difficult to read Capturing too little data can result in incomplete maps and faulty analysis

  10. Data Dictionary Three steps in developing a data dictionary: • Identify features to be observed and mapped • Determine attributes for each feature • Test the data dictionary

  11. Identify Features to Map • Target features are specific to the application • Reference features provide context and quality control Paths are the reference Grave markers are the target Trees are the target

  12. Identify Features to Map Tree Grave Markers Path

  13. Identify Features to Map • All features must be either a point, a line, or a polygon • Decision depends on the use of the data and the scale at which it will be displayed Buildings as points Buildings as areas

  14. Identify the Attributes to Record Roof Type Column type Construction Material Architectural Style ID Number Construction Dates Name of Structure

  15. Identify Attributes to Record • Use only attributes that are recognizable in the field • Limit attributes to those addressing the research questions • Make sure surveyors are familiar with the resources being mapped • Always have a unique GPS ID number for every target feature

  16. Identify Attributes to Record Attribute Formats • Menu • Numeric • Text • Date (auto generated) • Time (auto generated) • Attribute values • Should be observable • Avoid over reliance on “good, fair, poor” values • Be sure values are distinct from each other • Strive for operational definitions

  17. Determine Attributes to Record • Menu Attributes • Text Attributes • Standardize choices • Reduce errors • Easy to query • Not flexible • Must be well thought out Very Flexible Responsive to unanticipated conditions Difficult to query More typos

  18. Building the Data Dictionary • Build the data dictionary in your software • Replicate in a GeoDatabase structure • Build the GeoDatabase through GPS Analyst extension in ArcGIS and convert into a data dictionary • Build the data dictionary in your software and convert into a GeoDatabase through GPS Analyst extension in ArcGIS

  19. Test the Data Dictionary • Expect to revise • Add/Subtract features • Add/Subtract attributes • Add/Subtract attribute values • Refine the Data Dictionary • Extraneous to essential • Subjective to objective • Vague to operational definitions