Calculating a percent of a margin of error

elizfelter over 6 years ago

Dear community,

I am looking for guidance on calculating a percent of a margin or error. My work involves analyzing potential population risk to flooding, where I geospatially overlay block groups with flood zones in ArcGIS. If, for example, a block group is 75% covered by a flood zone, can I apply that percent to both the population estimate and the margin of error?

Thanks very much for your help!

Elizabeth

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Beth Jarosz over 6 years ago

Good morning Elizabeth -
I might propose an entirely different approach -- using population-weighted centroids for the spatial analysis. (What if the entire population is in the 25% of the block group land area that is outside the floodplain?) If the centroid falls within the floodplain, I'd assign the population to the floodplain, if outside, I would exclude the population from the floodplain.

The centroid method, of course, introduces its own kind of potential error, so you could always run the analysis both ways and report a range?

You can find the block group weighted centroids here:
www.census.gov/.../centersofpop.html
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Beth Jarosz over 6 years ago

Good morning Elizabeth -
I might propose an entirely different approach -- using population-weighted centroids for the spatial analysis. (What if the entire population is in the 25% of the block group land area that is outside the floodplain?) If the centroid falls within the floodplain, I'd assign the population to the floodplain, if outside, I would exclude the population from the floodplain.

The centroid method, of course, introduces its own kind of potential error, so you could always run the analysis both ways and report a range?

You can find the block group weighted centroids here:
www.census.gov/.../centersofpop.html
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