Hello there,

I need help with sorting out a problem. I want to see the sum of the length of multiple polylines that fall within a polygon.

I have a project where I have a polygon that overlaps a portion of Europe. The shape & size of this polygon is based on data from an authority, and the same authority claims that the area of the polygon is around 750 000 square kilometers. When comparing the created polygon in ArcGIS with the authority's representation of it online visually, it looks about right, but the computed area in ArcGIS is around 3,2 million square kilometres. Any ideas of this discrepancy? The polygon and basemap use the same projections -

The problem above is a parenthesis, that might, or might not be involved in the important question of this thread, below.

I have a lot of raw data that I want to evaluate. The data contains two sets of coordinates for 280 000 rows; for each row a pair of starting long/lat and a pair of ending long/lat. An example of a cell value is 54,3333. I have imported this data to ArcGIS with the XY to line Toolbox,

Originally, when I imported with the same projection as the rest of the project, the lines end up near the zero-meridian, west of Africa. I found out that the lines are placed correctly when

Next step (using the correclty placed line in the incorrect coordinate system), to calculate the length of the lines, first I used Intersect tool. No problems here - a new polygon withonly the lines within. After that, I use Spatial Join, and choose Sum for Shape_Length, and evaluate this cell in the resulting shape.

The problem here is that I'm not sure anymore in what unit this result is, and whichever unit it is, I do not believe it is correct, since the area of the polygon is so far off what it should be.

Can I please get inputs (and corrections) regarding my method, so that I can be assured what I'm doing will result in a.. result.

Thanks!

Your best course of action would be (always?) to

use an appropriate projection for your projectthat covers the entire study area and preserves the main measurements of interest (area, distance, or angle). I'm not familiar with European projections, but I would guess that something like Europe Albers Equal Area Conic would be a good starting point. Figure out the unit of measurement and go from there.