The meaning will vary depending on context. While the quotation implies a perspective looking across the road, it doesn't literally need to be so.

If you wrote:

The detective was trying to get through the crowd that was now five deep with angry onlookers.

Here it's front to back (from the perspective of the detective), not side to side.

So from the perspective of the speaker it would be five (somethings) in his line of sight.

The meaning will vary depending on context. While the quotation implies a perspective looking across the road, it doesn't literally need to be so.

If you wrote:

The detective was trying to get through the crowd that was now five deep with angry onlookers.

Here it's front to back (from the perspective of the detective), not side by side.

So from the perspective of the speaker it would be five (somethings) in his line of sight.