diff --git a/IV/Makefile b/IV/Makefile
index 9a91ac0..7af8901 100644
--- a/IV/Makefile
+++ b/IV/Makefile
@@ -32,7 +32,9 @@ RIVERS = \
 		 salvis-douglas-64-50k \
 		 salvis-visvalingam-64-50k \
 		 salvis-douglas-64-chaikin-50k \
-		 salvis-visvalingam-64-chaikin-50k
+		 salvis-visvalingam-64-chaikin-50k \
+		 salvis-overlaid-douglas-64-chaikin-50k \
+		 salvis-overlaid-visvalingam-64-chaikin-50k
 
 #################################
 # The thesis, publishable version
@@ -76,6 +78,7 @@ define FIG_template
 $(1).pdf: layer2img.py Makefile $(2)
 	python ./layer2img.py --outfile=$(1).pdf \
 		$$(if $$($(1)_WIDTHDIV),--widthdiv=$$($(1)_WIDTHDIV)) \
+		$$(if $$($(1)_QUADRANT),--quadrant=$$($(1)_QUADRANT)) \
 		$$(foreach i,1 2 3, \
 			$$(if $$($(1)_$$(i)SELECT),--group$$(i)-select="$$($(1)_$$(i)SELECT)") \
 			$$(if $$($(1)_$$(i)LINESTYLE),--group$$(i)-linestyle="$$($(1)_$$(i)LINESTYLE)") \
@@ -134,18 +137,25 @@ salvis-250k_WIDTHDIV = 10
 salvis-douglas-64-50k_2SELECT = wm_visuals where name='salvis-douglas-64'
 salvis-douglas-64-50k_WIDTHDIV = 2
 
-#salvis-visvalingam-64-50k_1SELECT = wm_visuals where name='salvis'
 salvis-visvalingam-64-50k_2SELECT = wm_visuals where name='salvis-visvalingam-64'
 salvis-visvalingam-64-50k_WIDTHDIV = 2
 
-#salvis-douglas-64-chaikin-50k_1SELECT = wm_visuals where name='salvis'
 salvis-douglas-64-chaikin-50k_2SELECT = wm_visuals where name='salvis-douglas-64-chaikin'
 salvis-douglas-64-chaikin-50k_WIDTHDIV = 2
 
-#salvis-visvalingam-64-chaikin-50k_1SELECT = wm_visuals where name='salvis'
 salvis-visvalingam-64-chaikin-50k_2SELECT = wm_visuals where name='salvis-visvalingam-64-chaikin'
 salvis-visvalingam-64-chaikin-50k_WIDTHDIV = 2
 
+salvis-overlaid-douglas-64-chaikin-50k_1SELECT = wm_visuals where name='salvis'
+salvis-overlaid-douglas-64-chaikin-50k_2SELECT = wm_visuals where name='salvis-douglas-64-chaikin'
+salvis-overlaid-douglas-64-chaikin-50k_WIDTHDIV = 2
+salvis-overlaid-douglas-64-chaikin-50k_QUADRANT = 4
+
+salvis-overlaid-visvalingam-64-chaikin-50k_1SELECT = wm_visuals where name='salvis'
+salvis-overlaid-visvalingam-64-chaikin-50k_2SELECT = wm_visuals where name='salvis-visvalingam-64-chaikin'
+salvis-overlaid-visvalingam-64-chaikin-50k_WIDTHDIV = 2
+salvis-overlaid-visvalingam-64-chaikin-50k_QUADRANT = 4
+
 
 .faux_test-rivers: tests-rivers.sql wm.sql Makefile .faux_db
 	bash db -v scaledwidth=$(SCALEDWIDTH) -f $<
diff --git a/IV/bib.bib b/IV/bib.bib
index 9357c7d..02bad4a 100644
--- a/IV/bib.bib
+++ b/IV/bib.bib
@@ -174,7 +174,7 @@
     title={Handbuch der Lehre von der Verteilung der Primzahlen},
     journal={Monatshefte f{\"u}r Mathematik und Physik},
     year={1911},
-    month={Dec},
+    month={12},
     day={01},
     volume={22},
     number={1},
diff --git a/IV/layer2img.py b/IV/layer2img.py
index 07f0d55..5517d38 100644
--- a/IV/layer2img.py
+++ b/IV/layer2img.py
@@ -48,17 +48,22 @@ def parse_args():
 
     parser.add_argument('--widthdiv',
                         default=1, type=float, help='Width divisor')
+    parser.add_argument('--quadrant', type=int, choices=(1,2,3,4))
 
     parser.add_argument('-o', '--outfile', metavar='<file>')
     return parser.parse_args()
 
 
-def read_layer(select, width):
+def read_layer(select, width, maybe_quadrant):
     if not select:
         return
     way = "way"
+    if maybe_quadrant:
+        way = "wm_quadrant(way, {})".format(maybe_quadrant)
+
     conn = psycopg2.connect(PSQL_CREDS)
     sql = "SELECT {way} as way1 FROM {select}".format(way=way, select=select)
+    print(sql)
     return geopandas.read_postgis(sql, con=conn, geom_col='way1')
 
 
@@ -80,9 +85,9 @@ def plot_args(geom, color, maybe_linestyle):
 def main():
     args = parse_args()
     width = TEXTWIDTH_CM / args.widthdiv
-    group1 = read_layer(args.group1_select, width)
-    group2 = read_layer(args.group2_select, width)
-    group3 = read_layer(args.group3_select, width)
+    group1 = read_layer(args.group1_select, width, args.quadrant)
+    group2 = read_layer(args.group2_select, width, args.quadrant)
+    group3 = read_layer(args.group3_select, width, args.quadrant)
     c1 = plot_args(group1, BLACK, args.group1_linestyle)
     c2 = plot_args(group2, ORANGE, args.group2_linestyle)
     c3 = plot_args(group3, GREEN, args.group3_linestyle)
diff --git a/IV/mj-msc.tex b/IV/mj-msc.tex
index cd2b7f4..6f80bff 100644
--- a/IV/mj-msc.tex
+++ b/IV/mj-msc.tex
@@ -231,7 +231,6 @@ smaller scale is worthy.
     \label{fig:salvis-generalized-50k}
 \end{figure}
 
-
 Figure~\onpage{fig:salvis-generalized-50k} illustrates the same river bend, but
 generalized using {\DP} and {\VW} algorithms. The resulting lines are jagged,
 thus the resulting line looks unlike a real river. To smoothen the jaggedness,
@@ -254,6 +253,21 @@ figure~\onpage{fig:salvis-generalized-chaikin-50k}.
     \label{fig:salvis-generalized-chaikin-50k}
 \end{figure}
 
+\begin{figure}[h]
+    \centering
+    \begin{subfigure}[b]{.49\textwidth}
+        \includegraphics[width=\textwidth]{salvis-overlaid-douglas-64-chaikin-50k}
+        \caption{Original and {\DP} + Chaikin's}
+    \end{subfigure}
+    \hfill
+    \begin{subfigure}[b]{.49\textwidth}
+        \includegraphics[width=\textwidth]{salvis-overlaid-visvalingam-64-chaikin-50k}
+        \caption{Original and {\VW} + Chaikin's}
+    \end{subfigure}
+    \caption{Generalized and smoothened river (1:50000) and the original one overlaid.}
+    \label{fig:salvis-overlaid-generalized-chaikin-50k}
+\end{figure}
+
 There are a few problems with {\VW} and {\DP} immediately visible in
 figure~\onpage{fig:salvis-generalized-chaikin-50k}:
 
diff --git a/IV/tests-rivers.sql b/IV/tests-rivers.sql
index c411619..b19e8c1 100644
--- a/IV/tests-rivers.sql
+++ b/IV/tests-rivers.sql
@@ -1,6 +1,6 @@
 \i wm.sql
 
--- wm_envelope clips a geometry by a bounding box around a given object,
+-- wm_bbox clips a geometry by a bounding box around a given object,
 -- matching dimensions of A-class paper (1 by sqrt(2).
 drop function if exists wm_bbox;
 create function wm_bbox(
@@ -22,6 +22,50 @@ begin
 end
 $$ language plpgsql;
 
+-- wm_quadrant divides the given geometry to 4 rectangles
+-- and returns the requested quadrant following cartesian
+-- convention:
+--  +----------+
+--  | II  | I  |
+--- +----------+
+--  | III | IV |
+--  +-----+----+
+-- matching dimensions of A-class paper (1 by sqrt(2).
+drop function if exists wm_quadrant;
+create function wm_quadrant(
+  geom geometry,
+  quadrant integer
+) returns geometry as $$
+declare
+  xmin float;
+  xmax float;
+  ymin float;
+  ymax float;
+begin
+  xmin = st_xmin(geom);
+  xmax = st_xmax(geom);
+  ymin = st_ymin(geom);
+  ymax = st_ymax(geom);
+
+  if quadrant = 1 or quadrant = 2 then
+    ymin = (ymin + ymax)/2;
+  else
+    ymax = (ymin + ymax)/2;
+  end if;
+
+  if quadrant = 2 or quadrant = 3 then
+    xmax = (xmin + xmax)/2;
+  else
+    xmin = (xmin + xmax)/2;
+  end if;
+
+  return st_intersection(
+    geom,
+    st_makeenvelope(xmin, ymin, xmax, ymax, st_srid(geom))
+  );
+end $$ language plpgsql;
+
+
 delete from wm_visuals where name like 'salvis%';
 insert into wm_visuals(name, way) values('salvis', (
     select st_intersection(