>From kitanderson@juno.com Fri Nov 13 17:53:16 PST 1998

The rules for mapping rivers in SOURCE OF THE NILE (AH) can be confusing.
The following flowchart rendering of the rules may therefore be helpful.

			MAPPING RIVERS

Definition:

acceptable hexside = a hexside bordering a hex that is a swamp, lake,
		     partially explored or blank or contains a river
		     connected to the same hexside. 

River Check Procedure:

IF CURRENT HEX IS A SWAMP OR A LAKE THEN
	exit
IF 2 OR MORE RIVERS FLOW OUT OF THE CURRENT HEX THEN
	roll 1 die
	IF RESULT IS 1 - 3 THEN
		hex is a lake
	IF RESULT IS 4 - 5 THEN
		hex is a swamp
	IF RESULT IS 6 THEN
		hex is a jungle/swamp
	exit
IF 1 OR MORE RIVERS FLOW DOWNSTREAM INTO CURRENT HEX THEN
	IF ONE RIVER FLOWS OUT OF THE CURRENT HEX THEN
		all rivers are connected
	exit
draw a card
IF AN ADJACENT HEX CONTAINS A RIVER LEADING TO CURRENT HEX THEN
	consult A
	IF RESULT IS RIVER CONTINUES THEN
0:		check first number at map: terrain 
		IF NUMBER DENOTES AN ACCEPTABLE HEXSIDE THEN
			draw river to that hexside
			goto 3
		ELSE
			goto 1
	ELSE IF RESULT IS RIVER ENDS THEN
1:		IF ENDING WOULD MEAN RIVER COULD NOT REACH A MOUTH THEN
			IF AT LEAST 1 ACCEPTABLE HEXSIDE EXISTS THEN
				goto 0
		IF ENDING WOULD MEAN RIVER COULD NOT MEET DRAINAGE REQ. THEN
			IF AT LEAST 1 ACCEPTABLE HEXSIDE EXISTS THEN
				goto 0
		ELSE IF CURRENT HEX IS A DESERT THEN
			goto 0
		ELSE
			draw river to center of hex
			mark with river source dot
			goto 3
	ELSE IF RESULT IS RIVER FORKS THEN
		check number(s) by map: terrain
		IF ONLY 1 NUMBER AND HEXSIDE IS ACCEPTABLE THEN
			river continues to that hexside
			goto 3
		ELSE IF 2 NUMBERS THEN
			IF BOTH HEXSIDES ARE ACCEPTABLE THEN
				draw river to continues to both hexsides
				goto 3
			ELSE IF ONLY 1 HEXSIDE ACCEPTABLE THEN
				draw river to continue to that hexside
				goto 3
			ELSE IF BOTH HEXSIDES UNACCEPTABLE THEN
				goto 1
ELSE
	consult B
	IF RESULT IS NO RIVER THEN
		exit
	IF RESULT IS RIVER BEGINS THEN
2:		check map: terrain first number
		IF ACCEPTABLE HEXSIDE THEN
			draw in river source leading to that hexside
			goto 3
		exit
	ELSE IF RESULT IS RIVER BEGINS OR EXTENDS THEN
		IF NO ADJACENT SWAMPS OR LAKES THEN
			goto 2
		ELSE IF 1 ADJACENT SWAMP OR LAKE THEN
			draw river from lake or swamp to center of hex
			goto 0
		ELSE IF > 1 SWAMP OR LAKE ADJACENT THEN
			choose a lake or swamp hexside randomly
			draw river from lake or swamp to center of hex
			goto 0
	ELSE IF RESULT IS RIVER CROSSES THEN
		check number(s) at map: terrain
		IF BOTH NUMBERS INDICATE ACCEPTABLE HEXSIDES THEN
			draw river between those hexsides
			draw arrow showing flow from first to second
			goto 3
		ELSE IF THERE IS ONLY 1 NUMBER THEN
			goto 2
		ELSE IF 1 OF THE 2 NUMBERS IS UNACCEPTABLE THEN
			goto 2
		ELSE IF ALL NUMBERS ARE UNACCEPTABLE THEN
			exit
3:IF YOU HAVE CONSTRUCTED A RIVER THAT FLOWS BACK INTO ITSELF THEN
	roll 1 die
	IF RESULT IS 1 - 5 THEN 
		change hex's terrain to swamp
	ELSE IF RESULT IS 6 THEN
		change hex's terrain to jungle/swamp
		
by Tom Anderson, 1998