r.weight(1)		      Grass User's Manual		   r.weight(1)



NNAAMMEE
       rr..wweeiigghhtt  - Raster map overlay program.
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..wweeiigghhtt

DDEESSCCRRIIPPTTIIOONN
       _r_._w_e_i_g_h_t  is a language driven raster map overlay program.  It provides
       a means for performing geographical analyses using several raster maps.
       _r_._w_e_i_g_h_t  asks the user to weight (assign numeric values to) the raster
       map categories of interest.  The assignment of weighted values requires
       that the user intimately understand the analysis being undertaken.  How
       important is the slope of the land in comparison with the current  land
       use,  or  the depth to bedrock?	The assignment of values to the land's
       characteristics allows _r_._w_e_i_g_h_t to mix and compare apples and  oranges,
       such as slopes and land uses, and soil types and vegetation.


       _r_._w_e_i_g_h_t  is  a	language-driven  analysis tool.  It responds to worded
       commands typed at the terminal.	Help is always available via  the  one
       word  command:  hheellpp.  Commands available in _r_._w_e_i_g_h_t are listed below.


       Note that raster map names appear in parentheses.  The use of parenthe-
       ses is now optional in _r_._w_e_i_g_h_t.

       _l_i_s_t _m_a_p_s
	      List available raster maps

       _l_i_s_t _c_a_t_e_g_o_r_i_e_s _(_n_a_m_e_)
	      List categories for raster map (name)

       _l_i_s_t _s_a_v_e
	      List saved analyses

       _l_i_s_t _a_n_a_l_y_s_i_s
	      Display current analysis request

       _p_r_i_n_t _a_n_a_l_y_s_i_s
	      Send current analysis request to printer

       _c_h_o_o_s_e _(_n_a_m_e_)
	      Choose raster map (name) for analysis

       _a_s_s_i_g_n _(_n_a_m_e_)
	      Interactive way to assign weights for raster map (name)

       _a_s_s_i_g_n _(_n_a_m_e_) _(_c_a_t_) _(_v_a_l_)
	      Assign weight (val) to category (cat) for raster map (name)

       _a_s_s_i_g_n _(_n_a_m_e_) _(_c_a_t_) _(_c_a_t_) _(_v_a_l_)
	      Assign  weight  (val)  to  categories (cat) (cat) for raster map
	      (name)

       _s_a_v_e   Save the current analysis

       _r_e_c_o_v_e_r
	      Recover old analysis

       _a_d_d    Request that weights be added (this is the default)

       _m_u_l_t   Request that weights be multiplied

       _e_x_e_c_u_t_e
	      Run analysis

       _e_r_a_s_e  Erase the screen

       _c_o_l_o_r _g_r_e_y
	      Set the graphics montior colors to a grey  scale	(this  is  the
	      default)

       _c_o_l_o_r _w_a_v_e
	      Set the graphics monitor colors to a color wave.

       _c_o_l_o_r _r_a_m_p
	      Set the graphics monitor colors to a color ramp.

       _q_u_i_t   Leave _r_._w_e_i_g_h_t

       A  more	detailed  explanation  of a command can be obtained by typing:
       hheellpp ((ccoommmmaanndd))


SSUUGGGGEESSTTEEDD AAPPPPRROOAACCHH
       In order for _r_._w_e_i_g_h_t to generate raster maps useful for analysis,  the
       user  must  make  a reasonable and defensible request.  While much more
       powerful than _r_._c_o_m_b_i_n_e, _r_._w_e_i_g_h_t is also  more	dangerous.   The  user
       provides  the  necessary  value	judgements  which  are	registered  as
       weights.  Only well-conceived value judgements will result in  defensi-
       ble  results.   We suggest the following approach to a weighted overlay
       analysis:

       STEP 1: BEFORE RUNNING WEIGHT

       a) Define the question to be answered.  e.g.,
	      sites suitable for building apartments."

       b) Determine what mapped information is useful for
	      answering  the  question.   e.g.,  geology,   soils,   land_use,
	      flood_potential.

       c) Based on professional judgement, statistical
	      inference,  and  engineering  principals,  assign weights to the
	      categories in the chosen raster maps.


       STEP 2: CHOOSE CELL MAPS


       In _r_._w_e_i_g_h_t, use the command _c_h_o_o_s_e to identify up to six  raster  maps
       of interest.



       STEP 3: ASSIGN WEIGHTS


       Using  the  _r_._w_e_i_g_h_t  command _a_s_s_i_g_n, assign specific weights to raster
       map categories.



       STEP 4: SAVE ANALYSIS


       Use the _s_a_v_e command to save a copy of the analysis requested for later
       use.



       STEP 5: RUN ANALYSIS


       Use _e_x_e_c_u_t_e to run the analysis.



       STEP 6: EVALUATE RESULTS


       To  modify  an  existing  analysis  request, use the _r_e_c_o_v_e_r command to
       retrieve the analysis and then go to STEP 3.


SSEEEE AALLSSOO
       GGRRAASSSS TTuuttoorriiaall:: rr..wweeiigghhtt


       _r_._i_n_f_e_r

       _r_._c_o_m_b_i_n_e

       _r_._m_a_p_c_a_l_c

AAUUTTHHOORR
       James Westervelt, U.S.Army Construction Engineering Research Laboratory

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_4 _$



GRASS 5.0							   r.weight(1)
