There are two questions: whether a point is within a region and an online tool to visualize a region by some kind of map.

Google Earth can be used to handle the second question. I presume that there are others.

There are many cases for the first question depending on the complexity of the region.

In the most complex cases, even mathematics has multiple definitions. Please, see: “How to find whether a point is inside or outside the region?”, “Nonzero-rule”, and “Even–odd rule”.

In the case of simple polygons, it becomes simpler. A simple polygon is one where none of the edges cross over each except at the defining vertices. Now for a mathematics lesson. Using analytic geometry, a line can be expression as: y=m x + b, e.g., y=(2/3)x+(5/7). We’re going to use a slightly more general form a x+b y+c=0, as this form also allow easy representation of vertical and horzontal lines. If one inserts the coordinates of an arbitary point into the left side expression and evaluates the expression, one gets a signed number. The magnitude of that number is the perpendicular distance of the point from the line. The sign of that number indicates which side of the line that the point is on. For each edge of the polygon, one can compute that expression. To determine what sign is desired, substitute in the coordinate any one of the other vertices’ coordinates. It doesn’t matter which vertex as they all have to be on one side as the shape is simple. Note the sign of the result. Then, do the point in question. If the sign is the same, then the point is on the correct side of that edge. Repeat this process for all the edge until either it fails for an edge, in ehich case, the point is outside or all edges pass, in which case the point is inside. You will need to decide whether a zero result edge test is inside or not and that is your decision as the point is on that edge. The other edge test still need to be done though.

In the case of a simple axis aligned rectangle, those edge line equations become even simpler. The four edge tests become the point’s longitude is greater than or (possibly equal to, see the comment of a zero edge test result above) the longitude of the left edge of the rectangle, the point’s longitude is less than or (possibly equal to, see the comment of a zero edge test result above) the longitude of the right edge of the rectangle, the point’s latitude is greater than or (possibly equal to, see the comment of a zero edge test result above) the latitude of the bottom edge of the rectangle, and the point’s latitude is less than or (possibly equal to, see the comment of a zero edge test result above) the longitude of the top edge of the rectangle. In the case of negative numbers, just use the usual comparison rules. Think of a number line extending from negative infinity on the left to positive infinity on the right. If a value m is to the left of a value n, then m is less than n. If a value m is to the right of a value n, then m is greater than n. If they equal they are equal.

I believe that answers the question. If it doesn’t, then try again.