Help with Intersect / Intersection Attribute Rule

[Robswann]

Hello, I am trying to determine the correct rule code for determining the amount of acreage within another polygon. 

For Example: I have a feature named Tracts that may or may not contain floodplain acreage (Feature name Floodplain). 

Could someone help me out? ..... This is what I have now.... but it is not pulling the correct acreage, and I think the correct function would be INTERSECTION, but not sure.

Thanks again

VAR FLOODPLAIN = FeatureSetByName($datastore, "RES_FLOOD_HAZARD")

VAR INTERSECTSFLOOD = INTERSECTS($FEATURE,FLOODPLAIN)

area(intersectsflood, 'acres')

[jcarlson · Accepted solution]

You guess correctly, you'll need Intersection to get the geometry of the overlapping area. However, this function requires two geometries as parameters, and you're working with a FeatureSet.

Simple Version: Getting Intersection of Single Feature

var floodplain = FeatureSetByName($datastore, "RES_FLOOD_HAZARD")

// Grab the first item for the intersects featureset
var flood_feat = First(Intersects($FEATURE, floodplain))

// Get intersection, calculate area
var xs = Intersection(flood_feat, $feature)

// Calculate acreage
return Area(xs) // multiply by some value, depending on the area units in use

However, a single tract may intersect with multiple flood zones, and we may want to capture this information.

Complex: Return a List of Intersected Areas

var floodplain = FeatureSetByName($datastore, "RES_FLOOD_HAZARD")

// Get FeatureSet of intersecting flood zones
var flood_fs = Intersects($FEATURE, floodplain))

// Instantiate output string
var out_str = 'Flood Zone Acreage:'

// Iterate over FeatureSet
for(var f in flood_fs){
    // Get intersection, calculate area
    var xs = Intersection(f, $feature)

    // Calculate acreage
    var a = Area(xs) // multiply by some value, depending on the area units in use

    // Append to output string
    out_str += `\n${f.flood_zone_identifier_field} | ${a} ac`
}

return out_str

This will return something like

Flood Zone Acreage:
Zone AE | 12.1 ac
Zone X | 6.23 ac 

[Robswann]

Thanks again for the help. For some reason the expression states it is valid, but will not save? I have tried everything from saving closing out, restarting ? 

[Robswann]

Thanks @jcarlson.  Any way I could just sum all the zones within that feature to return a value of the total flood acreage? 

[jcarlson · Accepted solution]

Oh, sure! Instead of an output string, you could just use a numeric value. Make these changes to the "complex" expression and see how it works.

Line  7 → var out_area = 0
...
Line 18 → out_area += a
...
Line 21 → return out_area

So instead of creating a cumulative string, you're adding up cumulative sum.

[Robswann]

This is very helpful. Thanks again!

[Robswann]

Thanks I figured it out, any way I could just sum all the zones within that feature?