gc ASCII: @ (sometimes works similarly, such at for 'at' as a preposition)
This small base shape in the right bottom of the frame is catching the following (the right side) characters,
and pointing the left direction. This indicates a preposition.
( 右側からつかんで左に働きかける補助的な小さな形)
. . . .

Open the extended index and middle fingers diagonally inward. 
( 間をひらいた人差し指と中指を斜め内側に向けて伸ばす)

name: [di] di sound of dim ( ディ )

definition (grammar):

Base overlays with #gc :

To work like an English preposition adding the meaning of the other character in the base overlay.
The examples of the base overlay and the meaning are following.

Related to a direction or a location 方向や位置にかかわって;

{gc,17(upper direction)} : above (touching or not does not the matter,
so sometimes it includes on also. (〜の上に(の)
(: the cloud above it) is the same to .
Combining another character on top of this base overlay, , more detail of 'above' can be explained.

{+{08,17}(low)}: low above (〜のやや上の/に)
{+{07,17}(high)}: high above (〜のずっと高いところの/に)
{+{17,01}(the highest point)}: at the summit/top of (〜のてっぺんの/に)
{+17,{03,31(shape)}(diagonal)}: diagonally above (something) (〜の斜め上の/に)

{+18(down, under, lower direction)}: below (〜の下の/に)
{+19(inner direction)}: in, inside of (〜の中の/に)
{+20(outer direction)}: out, out side of (〜の外の/に)
{+61(front direction)}: in front of (〜の前の/に)
{+62(back, behind)}: behind, in the back of (〜の後ろの/に)
{+(01,28}(center)}: in the center of (〜の真中の/に)
{+{17,28}the upper surface}: on (the upper surface of) (〜の上面の/に)
{+{02,19}(the left)}: on the left of (〜の左側の/に)
{+{02,20}(the right)}: on the right of (〜の右側の/に)
{+{19,28}(the reverse side)} : in the reverse side of (〜の裏側の/に)
{+{01,48}(circumference)}: around (〜のまわりの/に)
{+{01,70}(halfway, amid)}: between or among (〜の間の/に) Related to relation and comparison関係・比較にかかわって:
{+21(the heading direction)}: to, for (〜へ/の)
{+22(the returning or original direction)} : from (〜から(の))
{+14(way)}: through (〜を通って/通じての))
{+{14,70}going over}: beyond (〜を超えて)
{+14(through, way),22(origin, cause)}: because of (〜の理由で/の)
{+{13,21}(situation of parallel)}: along (〜に沿った/て)
{+11(limited)}: until (〜まで/の))
{+46(work)}: by, by the work (function) of (〜による/よって)
{+45(relation)}: about, related to (〜について(の))
{+{28(surface),45(relation)}(touch)}: touching to (〜に接して/た)
{+05(not)}: without (no joining of the following word originally) (〜なしで(の))
{+06(opposite)}: in spite of (〜にもかかわらず)
{+13(equal)}: as (well) as, in the same way of (〜とおなじく)
{+{13,15}(similar: the same type of recognition)}: like..., in the similar way of (〜と同様に/の)
{+{07,08}degree, level: as how much or little}:
(when the following word has a shape), in the size of;
(when the following word has some particular level or quality), in the degree of (〜ほどに/の)
{+25(joined)}: with (〜で、〜とともに、〜つきの)
{+04(minus)}: lacking, without
(the following word was joining originally but not for this time) (〜を欠かして/た)
{+{13,07}(more)}: more than; this meaning flexibly changes according to what follows next;
e.g.: (when the following word relates to length): longer than, (in case relating to area): wider than, etc. (〜以上に/の)
{+{13,08}(less)}: less than (〜以下に/の)
{+{13,17}(upper)}: upper than (〜より上に/の)
{+{13,18}(lower)}: lower than (〜より下に/の)
{+{13,61}(further ahead)}: further ahead of (〜より前に/の)
{+{13,61}(further behind)}: further behind of (〜より後ろに/の)
{+{13,19}(inner)}: inner than (〜より内側に/の)
{+{13,{02,19}(left)}: farther left of (〜より左側に/の)
{gc (preposition),64(emphasize)}: even at/in.. (modifying front word with the following words)

Related to Place, Time or Condition (場所・時・条件などにかかわって)

{+10(place)}: at, in, on, where( as a relative adverb) (〜(場所)で/〜の)
{+{10(place),22(origin)}(the departure point)}: starting from (出発地が〜の)
{+{10,21(heading)}(destination, where about)}: bound for (〜行きの)
{+36(time)}: at (for 'time'), when (as a relative adverb) (〜のときに/の)
{+{36,61} later)}: after (〜の(時間的に)後に/の)
{+36,62}(earlier)}: before (〜の(時間的に)前に/の)
{+13(same),36(time)}: at the same time as (〜と同時に/の)
{+{36,70}(time space in between)}: while, during (〜の(時)間に/の)
{+53(situation)}: as (the condition of ...) (preposition) (〜なふうで/に)
{+11limit, 21to}: until (〜までの/に)
{+ tentative} (a phrase): in case if (the phrase)(仮に〜なら 後続語は仮定の条件)
{ + (stress)} (a phrase): even if ... (...だったとしてさえ)
{+15(recognition}: as (being considered) (〜として(の))

More prepositions can be created freely, but simpler is better to see.

Compounding with verb-symbols:

changes these verb phrases into qualifiers similarly to various English ...ing forms: e.g.
, , , , , , ....

. . .