score:1

Accepted answer

As @roughnex said in the comments, the following line:

l.Element("latitude") != null || l.Element("longitude") != null

needs to be changed to:

l.Element("latitude") != null && l.Element("longitude") != null

The reason for this is how boolean logic works.

In your code, you have the following conditional statement:

l.Element("latitude") != null || l.Element("longitude") != null
&& (Double)l.Element("latitude") >= southLat 
&& (Double)l.Element("latitude") <= northLat
&& (Double)l.Element("longitude") >= westLong
&& (Double)l.Element("longitude") <= eastLong

but let's cut out the details and make it simpler where each letter is a condition:

A || B && C && D && F

When it's reduced to simpler terms, it is easier to see that if A resolves to True, then the rest of the conditional is ignored. That is why you were getting results that were outside of your desired area, because their latitude wasn't null.

score:0

For reference, this is a programming concept called short-circuiting. In boolean logic, if you have a condition

A || B

and A evaluates to true, then B won't be evaluated because the expression (A || B) will be true regardless of B's value. Similarly, if

A && B

and A evaluates to false, then B is not evaluated because the entire expression will evaluate to false, regardless of B's value. (False && true will always be false.)

Alternatively, if

A || B 

and A is false, then B must be evaluated, because in an OR comparison, only one has to be true for the whole expression to be true (False || True will be True). So since A is false, there's still a chance that B could be true, so we have to check.


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