I am looking to create plot boundaries with multi-polygons, is this possible in collect earth online? We could split these multi-polygons into single polygons, however that would cause the number of plots to increase by a lot.


asked 08 Jul '21, 21:51

kl799's gravatar image

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Hi there,

You cannot use multi-part polygons to define plots in CEO. However, to reduce the number of plots you could create plots that incorporate the area of all the parts of a multi-polygon and then split the multi-polygons into single polygons and use those as samples.

Hope this helps, Karen

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answered 08 Jul '21, 22:54

kdyson's gravatar image

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Also, Karen's point about making larger single polygon plots and using your multipolygons (split into multiple single polygons) as sample shapes within the larger plots is a valid solution within CEO.

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answered 09 Jul '21, 17:28

gjohnson's gravatar image

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Hi kl799,

We have never used multi-polygons for plot boundaries before. While the web application may actually be able to store and render them in the UI, this is not how CEO is meant to be used.

An AOI (Area of Interest) is a rectangular box on the map, which delineates the area in which you intend to collect survey data.

A Plot is a small (often circular or square) region within the AOI in which a user will be presented with satellite imagery and asked to answer survey questions about what they see within the plot boundary.

A Sample is a location within a plot (often a point) to which survey answers are geographically attached.

Usually, a project designer will create a new project over their area of interest (e.g., a province in China). They will specify a number of plots within this area at which they want to collect data (e.g., 500 small square plots, randomly distributed within the AOI, equally spaced out on a grid, or coming from an uploaded CSV or Shapefile). Then they would specify a number of samples within each plot (e.g., 10-100 sample points per plot, randomly distributed within the plot boundary, equally spaced out on a grid, or coming from an uploaded CSV or Shapefile).

A user who wishes to collect data for this project navigates to the collection page and clicks the "Go to first plot" button, which zooms the map to the first unanalyzed plot, displays satellite basemap imagery, and draws the plot boundary and sample points on top of it. The user then selects one or more sample points within the plot and answers the survey questions in the right-hand sidebase, thereby assigning their answers to the selected sample points (e.g., These sample points are on Agriculture. These other sample points are on Forest.) The process of selecting sample points and assigning values to them is repeated until all questions have been answered for all points. Then the plot data is saved, and the user can proceed to the next plot.

When data collection is complete, the project designer can navigate to the review project page to download two CSVs of all the survey answers provided by their users. One CSV includes one row per sample point with columns for each of the questions and their answers. The other CSV includes one row per plot, which provides a distribution of the answers assigned to the samples in that plot for each question (e.g., Question: What is the Land Cover?, Answer Distribution: 80% Forest, 10% Agriculture, 10% Water).

I hope this helps to clarify how CEO's data collection features are meant to be used.

Best, Gary

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answered 09 Jul '21, 17:26

gjohnson's gravatar image

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question asked: 08 Jul '21, 21:51

question was seen: 1,541 times

last updated: 09 Jul '21, 17:28