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  cate-
       gories  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 charac-
       teristics 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 parentheses 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 defensible 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)
